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Polynomial

Class 9th Mathematics West Bengal Board Solution
Let Us Work Out 7.1
  1. Let us write which are the polynomials in the following algebraic expressions. Let us…
  2. In the following polynomials, let us write which are first degree polynomials in one…
  3. Let us write the co-efficient of the following polynomials according to the guidelines:…
  4. I write the degree of each of the following polynomials: (i) x^4 + 2x^3 + x^2 + x (ii)…
  5. I write two separate binomials in one variable whose degrees are 17.…
  6. I write two separate monomials in one variable whose degrees are 4.…
  7. I write two separate trinomials in one variable whose degrees are 3.…
  8. In the following algebraic expressions, which are polynomials in one variable, which…
Let Us Work Out 7.2
  1. If f(x) = x^2 + 9x - 6, then let us write by calculating the values of f(0), f(1) and…
  2. f(x) = 2x^3 + x^2 + x + 4 By calculating the following polynomials f(x) let us write…
  3. f(x) = 3x^4 - 5x^3 + x^2 + 8 By calculating the following polynomials f(x) let us…
  4. f(x) = 4 + 3x - x^3 + 5x^6 By calculating the following polynomials f(x) let us write…
  5. f(x) = 6 + 10x - 7x^2 By calculating the following polynomials f(x) let us write the…
  6. The zero of the polynomial P(x) = x - 1 is 1. Let us check the following statements—…
  7. The zero of the polynomial P(x) = 3 - x is 3. Let us check the following statements—…
  8. The zero of the polynomial P(x) = 5x + 1 is - 1/5 Let us check the following…
  9. The two zeros of the polynomial P(x) = x^2 - 9 are 3 and -3. Let us check the…
  10. The two zeros of the polynomial P(x) = x^2 - 5x are 0 and 5. Let us check the…
  11. The two zeros of the polynomial P(x) = x^2 - 2x - 8 are 4 and (-2). Let us check the…
  12. f(x) = 2 - x Let us determine the zeros of the following polynomials—…
  13. f(x) = 7x + 2 Let us determine the zeros of the following polynomials—…
  14. f(x) = x + 9 Let us determine the zeros of the following polynomials—…
  15. f(x) = 6 - 2x Let us determine the zeros of the following polynomials—…
  16. f(x) = 2x Let us determine the zeros of the following polynomials—…
  17. f(x) = ax + b, (a ≠ 0) Let us determine the zeros of the following polynomials—…
Let Us Work Out 7.3
  1. x - 2 By applying Remainder Theorem, let us calculate and write the remainder that I…
  2. x + 2 By applying Remainder Theorem, let us calculate and write the remainder that I…
  3. 2x - 1 By applying Remainder Theorem, let us calculate and write the remainder that I…
  4. 2x + 1 By applying Remainder Theorem, let us calculate and write the remainder that I…
  5. x^3 - 6x^2 + 13x + 60 By applying Remainder Theorem, let us calculate and write the…
  6. x^3 - 3x^2 + 4x + 50 By applying Remainder Theorem, let us calculate and write the…
  7. 4x^3 + 4x^2 - x - 1 By applying Remainder Theorem, let us calculate and write the…
  8. 11x^3 - 12x^2 - x + 7 By applying Remainder Theorem, let us calculate and write the…
  9. the polynomial x^3 - 6x^2 + 9x - 8 is divided by (x - 3) Applying Remainder Theorem,…
  10. the polynomial x^3 - ax^2 + 2x - a is divided by (x - a) Applying Remainder Theorem,…
  11. Applying Remainder Theorem, let us calculate whether the polynomial. P(x) = 4x^3 + 4x^2…
  12. For what value of a, the divisions of two polynomials (ax^3 + 3x^2 - 3) and (2x^3 - 5x…
  13. The two polynomials x^3 + 2x^2 - px - 7 and x^3 + px^2 - 12x + 6 are divided by (x + 1)…
  14. If the polynomial x^4 - 2x^3 + 3x^2 - ax + b is divided by (x - 1) and (x + 1) and the…
  15. If f (x) = a (x-b)/a-b + b (x-a)/b-a then let us show that, f(a) + f(b) = f(a + b)…
  16. If f(x) = ax + b and f(0) = 3, f(2) = 5, then let us determine the values of a and b.…
  17. If f(x) = ax^2 + bx + c and f(0) = 2, f(1) = 1 and f(4) = 6, then let us calculate the…
  18. Which of the followings is a polynomial in one variable?A. x + 2/x + 3 B. 3 root x +…
  19. Which of the following is a polynomial?A. x - 1 B. x-1/x+1 C. x^2 - 2/x^2 + 5 D. x^2…
  20. Which of the followings is a linear polynomial?A. x + x^2 B. x + 1 C. 5x^2 - x + 3 D.…
  21. Which of the followings is a second degree polynomial?A. root x-4 B. x^3 + x C. x^3 +…
  22. The degree of the polynomial root 3 isA. 1/2 B. 2 C. 1 D. 0
  23. Let us write the zero of the polynomial p(x) = 2x -3.
  24. If p(x) = x + 4, let us write the value of p(x) + p(-x).
  25. Let us write the remainder, if the polynomial x^3 + 4x^2 + 4x - 3 is divided by x.…
  26. If (3x - 1)^7 = a7x^7 + a6x^6 + a5x^5 + ………..+ a1x + a0, then let us write the value…
Let Us Work Out 7.4
  1. 2x^3 + 3x^2 - 1 Let us calculate and write, which of the following polynomials will…
  2. x^4 + x^3 - x^2 + 4x + 5 Let us calculate and write, which of the following…
  3. 7x^3 + x^2 + 7x + 1 Let us calculate and write, which of the following polynomials…
  4. 3 + 3x - 5x^3 - 5x^4 Let us calculate and write, which of the following polynomials…
  5. x^4 + x^2 + x + 1 Let us calculate and write, which of the following polynomials will…
  6. x^3 + x^2 + x + 1 Let us calculate and write, which of the following polynomials will…
  7. f(x) = x^4 - x^2 and g(x) = x + 2 By using Factor Theorem, let us write whether g(x)…
  8. f(x) = 2x^3 + 9x^2 - 11x - 30 and g(x) = x + 5 By using Factor Theorem, let us write…
  9. f(x) = 2x^3 + 7x^2 - 24x - 45 and g(x) = x - 3 By using Factor Theorem, let us write…
  10. f(x) = 3x^3 + x^2 - 20x + 12 and g(x) = 3x - 2 By using Factor Theorem, let us write…
  11. Let us calculate and write the value of k for which the polynomial 2x^4 + 3x^3 + 2kx^2…
  12. f(x) = 2x^3 + 9x^2 + x + k and g(x) = x - 1 Let us calculate the value of k for which…
  13. f(x) = kx^2 - 3x + k and g(x) = x - 1 Let us calculate the value of k for which g(x)…
  14. f(x) = 2x^4 + x^3 - kx^2 - x + 6 and g(x) = 2x - 3 Let us calculate the value of k for…
  15. f(x) = 2x^3 + kx^2 + 11x + k + 3 and g(x) = 2x - 1 Let us calculate the value of k for…
  16. Let us calculate and write the values of a and b if x^2 - 4 is a factor of the…
  17. If (x + 1) and (x + 2) are two factors of the polynomial x^3 + 3x^2 + 2ax + b, then let…
  18. If the polynomial ax^3 + bx^2 + x - 6 is divided by x - 2 and remainder is 4, then let…
  19. Let us show that if n is any positive integer (even or odd), x - y is a factor of the…
  20. Let us show that if n is any positive odd integer, then x + y is a factor of xn + yn.…
  21. Let us show that if n be any positive integer (even or odd), the x - y never be a…
  22. If the polynomial x^3 + 6x^2 + 4x + k is divisible by (x + 2), then the value of k…
  23. In the polynomial f(x) if f (- 1/2) = 0 then the factor of f(x) will beA. 2x - 1 B.…
  24. (x - 1) is a factor of the polynomial f(x) but it is not the factor of g(x). So (x -…
  25. (x + 1) is a factor of the polynomial xn + 1 whenA. n is a positive odd integer B. n…
  26. If n^2 - 1 is a factor of the polynomial an^4 + bn^3 + cn^2 + dn + e thenA. a + c + e…
  27. Let us calculate and write the value of a for which x + a will be a factor of the…
  28. Let us calculate and write the value of k for which x - 3 will be a factor of the…
  29. Let us write the value of f(x) + f(-x) when f(x) = 2x + 5.
  30. Both (x - 2) and (x - 1/2) are factors of the polynomial px^2 + 5x + r, let us…
  31. Let us write the zero of the linear polynomial f(x) = 2x + 3.

Let Us Work Out 7.1
Question 1.

Let us write which are the polynomials in the following algebraic expressions. Let us write the degree of each of the polynomials.

(i) 2x6 – 4x5 + 7x2 + 3

(ii) x–2 + 2x–1 + 4

(iii)

(iv)

(v) x51 – 1

(vi)

(vii) 15

(viii) 0

(ix)

(x) y3 + 4

(xi)


Answer:

(i) Since all the exponents (power) of variable(x) are whole no. (i.e., zero or positive integers)

⇒ 2x6 – 4x5 + 7x2 + 3 is a polynomial.


(Note: The degree is the value of the greatest (highest) exponent of any expression (except the constant) in the polynomial. To find the degree all that you have to do is find the largest exponent in the polynomial).


And, since here the highest power is 6,


⇒ It is a polynomial of degree 6.


(ii) Since all the exponents (power) of variable(x) are not whole no. (i.e., zero or positive integers)


⇒ x–2 + 2x–1 + 4 is not a polynomial.


(iii) Since all the exponents (power) of variable(y) are whole no. (i.e., zero or positive integers)


is a polynomial.


And, since here the highest power is 3,


⇒ It is a polynomial of degree 3.


(iv)



Since all the exponents (power) of variable(x) are not whole no.(i.e., zero or positive integers)


is not a polynomial.


(v) Since all the exponents (power) of variable(x) are whole no. (i.e., zero or positive integers)


⇒ x51 – 1 is a polynomial.


And, since here the highest power is 51,


⇒ x51 – 1 is a polynomial of degree 51.


(vi)


Since all the exponents (power) of t are not whole no.(i.e., zero or positive integers)


is not a polynomial.


(vii) 15 is a constant polynomial as there is no variable present in that.


And, therefore the highest power is 0


⇒ 15 is a polynomial with degree 0.


(viii) 0 is a constant polynomial (zero polynomial) as there is no variable present in that.


⇒ 0 is a polynomial with degree 0.


(ix)


Since all the exponents (power) of variable(z) are not whole no.(i.e., zero or positive integers)


is not a polynomial.


(x) Since all the exponents (power) of variable(y) are whole no. (i.e., zero or positive integers)


⇒ y3 +4 is a polynomial.


And, since here the highest power is 3,


⇒ y3 +4 is a polynomial of degree 3.


(xi)


Since all the exponents (power) of variable(x) are whole no.(i.e., zero or positive integers)


And, since here the highest power is 2


is a polynomial of degree 2.



Question 2.

In the following polynomials, let us write which are first degree polynomials in one variable, which are second degree polynomials in one variable and which are third degree polynomials in one variable.

(i) 2x + 17

(ii)x3 + x2 + x+ 1

(iii) –3 + 2y2 + 5xy

(iv)5 – x – x3

(v)

(vi)


Answer:

(i) (Note: The degree is the value of the greatest (highest) exponent of any expression (except the constant) in the polynomial. To find the degree all that you have to do is find the largest exponent in the polynomial).

Since, here the highest power of variable(x) is 1,


⇒ 2x + 17 is a first degree polynomial.


(ii) Since, here the highest power of variable(x) is 3,


⇒ x3 + x2 + x+ 1 is a third degree polynomial.


(iii) Since, here the highest power of variable(x, y) is 2,


⇒ –3 + 2y2 + 5xy is a second degree polynomial.


(Note: Whenever we have polynomial in two variable (i.e., x and y) and both are in multiplication we see for the degree by adding the powers of both the variable.)


(iv) Since, here the highest power of variable(x) is 3,


⇒ 5 – x – x3 is a third degree polynomial.


(v) Since, here the highest power of variable (t) is 2,


⇒ √2 +t+t2 is a second degree polynomial.


(vi) Since, here the highest and only power of variable(x) is 1,


⇒ √ 5x is a first degree polynomial.



Question 3.

Let us write the co-efficient of the following polynomials according to the guidelines:

(i) The co-efficient of x3 in 5x3 – 13x2 + 2

(ii) The co-efficient of x in x2 – x + 2

(iii) The co-efficient of x2 in 8x – 19

(iv) The co-efficient of x0 in


Answer:

(i) We can see that with x, the constant written before that is 5,

⇒ The co-efficient of x3 in 5x3 – 13x2 + 2 is 5.


(ii) We can see that with x, the constant written before that is -1,


⇒ The co-efficient of x in x2 – x + 2 is -1.


(iii) We can see that with x2, the constant written before that is 0, because there is no x2 in polynomial.


⇒ The co-efficient of x2 in 8x – 19 is 0.


(iv) We can see that with x0 (i.e., the constant) is √(11)


⇒ The co-efficient of x0 in √ (11) – 3√(11) x+x2 is √(11).



Question 4.

I write the degree of each of the following polynomials:

(i) x4 + 2x3 + x2 + x

(ii) 7x – 5

(iii) 16

(iv) 2 – y – y3

(v) 7t

(vi) 5 – x2 + x19


Answer:

(i) (Note: The degree is the value of the greatest (highest) exponent of any expression (except the constant) in the polynomial. To find the degree all that you have to do is find the largest exponent in the polynomial).

Since, here the highest power of variable is 4,


⇒ Degree of polynomial=4.


(ii) Since, here the highest power of variable is 1,


⇒ Degree of polynomial=1.


(iii) Since, here the highest power of variable is 0, because there exist no variable.


⇒ Degree of polynomial=0.


(iv) Since, here the highest power of variable is 3,


⇒ Degree of polynomial=3.


(v) Since, here the highest power of variable is 1,


⇒ Degree of polynomial=1.


(vi) Since, here the highest power of variable is 19,


⇒ Degree of polynomial=19.



Question 5.

I write two separate binomials in one variable whose degrees are 17.


Answer:

(Note: The degree is the value of the greatest (highest) exponent of any expression (except the constant) in the polynomial. To find the degree all that you have to do is find the largest exponent in the polynomial).

(Binomial means the polynomial will have two terms and degree =17 means that highest power should be 17).


∴ First binomial: x17 – 4x5


Second Binomial= 7x17 + 27



Question 6.

I write two separate monomials in one variable whose degrees are 4.


Answer:

(Note: The degree is the value of the greatest (highest) exponent of any expression (except the constant) in the polynomial. To find the degree all that you have to do is find the largest exponent in the polynomial).

(Monomial means the polynomial will have one term and degree =4 means that highest power should be 4).


∴ First binomial: xy3


Second Binomial=x4



Question 7.

I write two separate trinomials in one variable whose degrees are 3.


Answer:

(Note: The degree is the value of the greatest (highest) exponent of any expression (except the constant) in the polynomial. To find the degree all that you have to do is find the largest exponent in the polynomial).

(Trinomial means the polynomial will have three terms and degree 3 means that highest power should be 3).


∴ First binomial: 7 x3 – 4x -7


Second Binomial: x3+5x2-x



Question 8.

In the following algebraic expressions, which are polynomials in one variable, which are polynomials in two variables and which are not polynomials —Let us write them.

(i) x2 + 3x + 2

(ii) x2 + y2 + a2

(iii) y2 – 4ax

(iv) x + y + 2

(v) x8 + y4 + x5y9

(vi)


Answer:

(i) Since, here the highest power of variable is 1, which is a whole no.

⇒ x2 + 3x + 2is a polynomial.


But here only one variable, i.e., x is used,


⇒ x2 + 3x + 2 is a polynomial in one variable.


(ii) Since, here the highest power of variable is 2, which is a whole no.


x2 + y2 + a2 is a polynomial.


Since, here two variable, i.e., x and y are used,


⇒ x2 + y2 + a2 is a polynomial in two variables.


(iii) Since, here the highest power of variable is 2, which is a whole no.


⇒ y2 – 4ax is a polynomial.


Since, here two variable, i.e., x and y are used,


⇒ y2 – 4ax is a polynomial in one variable.


(iv) Since, here the highest power of variable is 1, which is a whole no.


⇒ x + y + 2 is a polynomial.


But here only two variable, i.e., x and y and are used,


⇒ x + y + 2 is a polynomial in one variable.


(v) Since, here the highest power of variable is( 5+9=14 ), which is a whole no.


(Note: 5 for x and 9 for y)


⇒ x8 + y4 + x5y9 is a polynomial.


here only two variable, i.e., x and y is used,


⇒ x2 + 3x + 2 is a polynomial in two variables.


(vi) Since, here the highest power of variable is 1, which is a whole no.



And, since the exponent of variable is not zero or whole number,


is not a polynomial.




Let Us Work Out 7.2
Question 1.

If f(x) = x2 + 9x – 6, then let us write by calculating the values of f(0), f(1) and f(3).


Answer:

Formula used/Theory.


Putting the value of ‘x’ in f(x) gives out the value of f(x) on ‘x’


We have,


f(x) = x2 + 9x – 6


When we put


x = 0


Then,


f(0) = 02 + 9 × 0 – 6


f(0) = –6


when we put


x = 1


Then,


f(1) = 12 + 9 × 1 – 6


f(1) = 10 –6


f(1) = 4


When we put


x = 3


Then,


f(3) = 32 + 9 × 3 – 6


f(3) = 9+27 –6


f(3) = 30


Conclusion.


The values of f(0), f(1), f(3) are –6, 4, 30 respectively.



Question 2.

By calculating the following polynomials f(x) let us write the values of f(1) and f(–1):

f(x) = 2x3 + x2 + x + 4


Answer:

Formula used/Theory.


Putting the value of ‘x’ in f(x) gives out the value of f(x) on ‘x’


We have,


f(x) = 2x3 + x2 + x + 4


When we put x = 1


Then,


f(1) = 2(1)3 + (1)2 + 1 + 4


f(1) = 2+1+1+4


f(1) = 8


When we put x = –1


Then,


f(-1) = 2(-1)3 + (-1)2 + (-1) + 4


f(-1) = (-2) +1–1+4


f(-1) = 2


Conclusion.


The value of f(1), f(-1) are 8, 2 respectively.



Question 3.

By calculating the following polynomials f(x) let us write the values of f(1) and f(–1):

f(x) = 3x4 – 5x3 + x2 + 8


Answer:

Formula used/Theory.


Putting the value of ‘x’ in f(x) gives out the value of f(x) on ‘x’


We have,


f(x) = 3x4 – 5x3 + x2 + 8


When we put x = 1


Then,


f(1) = 3(1)4 – 5(1)3 + (1)2 + 8


f(1) = 3 – 5 + 1 + 8


f(1) = 7


When we put x = -1


Then,


f(-1) = 3(-1)4 – 5(-1)3 + (-1)2 + 8


f(-1) = 3 – (-5) + 1 + 8


f(-1) = 3 + 5 + 1 + 8


f(-1) = 17


Conclusion.


The value of f(1), f(-1) are 7, 17 respectively.



Question 4.

By calculating the following polynomials f(x) let us write the values of f(1) and f(–1):

f(x) = 4 + 3x – x3 + 5x6


Answer:

Formula used/Theory.


Putting the value of ‘x’ in f(x) gives out the value of f(x) on ‘x’


We have,


f(x) = 4 + 3x – x3 + 5x6


When we put x = 1


Then,


f(1) = 4 + 3 × 1 – 1 + 5 × 1


f(1) = 4 + 3 – 1 + 5


f(1) = 11


When we put x = -1


Then,


f(-1) = 4 + 3 × (-1) – (-1)3 + 5 × (-1)6


f(-1) = 4 + 3 × (-1) – (-1) + 5 × (-1)


f(-1) = 4 – 3 + 1 + 5


f(-1) = 7


Conclusion.


The value of f(1), f(-1) are 11, 7 respectively.



Question 5.

By calculating the following polynomials f(x) let us write the values of f(1) and f(–1):

f(x) = 6 + 10x – 7x2


Answer:

Formula used/Theory.


Putting the value of ‘x’ in f(x) gives out the value of f(x) on ‘x’


We have,


f(x) = 6 + 10x – 7x2


when we put x = 1


then,


f(1) = 6 + 10 × (1) – 7(1)2


f(1) = 6 + 10 × 1 – 7 × 1


f(1) = 6 + 10 – 7


f(1) = 9


when we put x = -1


then,


f(-1) = 6 + 10 × (-1) – 7(-1)2


f(-1) = 6 + 10 × (-1) – 7 × 1


f(-1) = 6 – 10 – 7


f(-1) = -11


Conclusion.


The value of f(1), f(-1) are 9, -11 respectively.



Question 6.

Let us check the following statements—

The zero of the polynomial P(x) = x – 1 is 1.


Answer:

Formula used/Theory.


There is some value of ‘x’ for which the P(x) comes to 0, that value of ‘x’ is said to be zero of polynomial P(x)


We have,


P(x) = x-1


And zero of the polynomial P(x) is 1


Then,


Zero of the polynomial P(x)


Means P(x) = 0


x-1 = 0


x = 1


∴ Zero of polynomial P(x) is 1


Conclusion.


Hence, the statement is True



Question 7.

Let us check the following statements—

The zero of the polynomial P(x) = 3 – x is 3.


Answer:

Formula used/Theory.


There is some value of ‘x’ for which the P(x) comes to 0, that value of ‘x’ is said to be zero of polynomial P(x)


We have,


P(x) = 3 – x


And zero of the polynomial P(x) is 3


Then,


Zero of the polynomial P(x)


Means P(x) = 0


3 – x = 0


-x = -3


x = 3


∴ Zero of polynomial P(x) is 3


Conclusion.


Hence, the statement is True



Question 8.

Let us check the following statements—

The zero of the polynomial P(x) = 5x + 1 is


Answer:

Formula used/Theory.


There is some value of ‘x’ for which the P(x) comes to 0, that value of ‘x’ is said to be zero of polynomial P(x)


We have,


P(x) = 5x+1


And zero of the polynomial P(x) is


Then,


Zero of the polynomial P(x)


Means P(x) = 0


5x+1 = 0


5x = -1


x =


∴ Zero of polynomial P(x) is


Conclusion.


Hence, the statement is True



Question 9.

Let us check the following statements—

The two zeros of the polynomial P(x) = x2 – 9 are 3 and –3.


Answer:

Formula used/Theory.


There is some value of ‘x’ for which the P(x) comes to 0, that value of ‘x’ is said to be zero of polynomial P(x)


We have,


P(x) = x2 – 9


And zero of the polynomial P(x) are 3 and -3


Then,


Zero of the polynomial P(x)


Means P(x) = 0


x2 – 9 = 0


x2 – (3)2 = 0


⇒ a2 – b2 = (a+b)(a-b)


(x – 3)(x+3) = 0


x – 3 = 0 and x+3 = 0


x = 3 and x = -3


∴ Zero of polynomial P(x) is 3 and -3


Conclusion.


Hence, the statement is True



Question 10.

Let us check the following statements—

The two zeros of the polynomial P(x) = x2 – 5x are 0 and 5.


Answer:

Formula used/Theory.


There is some value of ‘x’ for which the P(x) comes to 0, that value of ‘x’ is said to be zero of polynomial P(x)


We have,


P(x) = x2 – 5x


And zero of the polynomial P(x) are 0 and 5


Then,


Zero of the polynomial P(x)


Means P(x) = 0


x2 – 5x = 0


x(x– 5) = 0


x = 0 and (x-5) = 0


⇒ x = 0 and x = 5


∴ Zero of polynomial P(x) is 0 and 5


Conclusion.


Hence, the statement is True



Question 11.

Let us check the following statements—

The two zeros of the polynomial P(x) = x2 – 2x – 8 are 4 and (–2).


Answer:

Formula used/Theory.


There is some value of ‘x’ for which the P(x) comes to 0, that value of ‘x’ is said to be zero of polynomial P(x)


We have,


P(x) = x2 – 2x – 8


And zero of the polynomial P(x) are 4 and -2


Then,


Zero of the polynomial P(x)


Means P(x) = 0


x2 – 2x – 8 = 0


As in quadratic eq


We have to divide (-2x) in 2 parts such that product comes to (-8x2)


Hence the factors are :-


(-x) × (8x) addition gives 8x – x = 7x


(-2x) × (4x) addition gives 4x – 2x = 2x


(-4x) × (2x) addition gives 2x – 4x = -2x


Hence factors are -4x and 2x


x2 – 4x + 2x – 8 = 0


x(x – 4)+2(x – 4) = 0


(x+2)(x – 4) = 0


x+2 = 0 and x – 4 = 0


x = (-2) and x = 4


∴ Zero of polynomial P(x) is 4 and -2


Conclusion.


Hence, the statement is True



Question 12.

Let us determine the zeros of the following polynomials—

f(x) = 2 – x


Answer:

Formula used/Theory.


There is some value of ‘x’ for which the f(x) comes to 0, that value of ‘x’ is said to be zero of polynomial f(x)


We have,


f(x) = 2 – x


Then,


Zero of the polynomial f(x)


Means f(x) = 0


2 – x = 0


-x = -2


x = 2


∴ Zero of polynomial f(x) is 2


Conclusion.


Hence, the zero of the polynomial f(x) is 2



Question 13.

Let us determine the zeros of the following polynomials—

f(x) = 7x + 2


Answer:

Formula used/Theory.


There is some value of ‘x’ for which the f(x) comes to 0, that value of ‘x’ is said to be zero of polynomial f(x)


We have,


f(x) = 7x+2


Then,


Zero of the polynomial f(x)


Means f(x) = 0


7x+2 = 0


7x = -2


x =


∴ Zero of polynomial f(x) is


Conclusion.


Hence, the zero of the polynomial f(x) is



Question 14.

Let us determine the zeros of the following polynomials—

f(x) = x + 9


Answer:

Formula used/Theory.


There is some value of ‘x’ for which the f(x) comes to 0, that value of ‘x’ is said to be zero of polynomial f(x)


We have,


f(x) = x+9


Then,


Zero of the polynomial f(x)


Means f(x) = 0


x+9 = 0


x = -9


∴ Zero of polynomial f(x) is –9


Conclusion.


Hence, the zero of the polynomial f(x) is –9



Question 15.

Let us determine the zeros of the following polynomials—

f(x) = 6 – 2x


Answer:

Formula used/Theory.


There is some value of ‘x’ for which the f(x) comes to 0, that value of ‘x’ is said to be zero of polynomial f(x)


We have,


f(x) = 6 – 2x


Then,


Zero of the polynomial f(x)


Means f(x) = 0


6 – 2x = 0


-2x = -6


x = = 3


∴ Zero of polynomial f(x) is 3


Conclusion.


Hence, the zero of the polynomial f(x) is 3



Question 16.

Let us determine the zeros of the following polynomials—

f(x) = 2x


Answer:

Formula used/Theory.


There is some value of ‘x’ for which the f(x) comes to 0, that value of ‘x’ is said to be zero of polynomial f(x)


We have,


f(x) = 2x


Then,


Zero of the polynomial f(x)


Means f(x) = 0


2x = 0


x = 0


∴ Zero of polynomial f(x) is 0


Conclusion.


Hence, the zero of the polynomial f(x) is 0



Question 17.

Let us determine the zeros of the following polynomials—

f(x) = ax + b, (a ≠ 0)


Answer:

Formula used/Theory.


There is some value of ‘x’ for which the f(x) comes to 0, that value of ‘x’ is said to be zero of polynomial f(x)


We have,


f(x) = ax+b


Then,


Zero of the polynomial f(x)


Means f(x) = 0


ax+b = 0


ax = -b


x =


∴ Zero of polynomial f(x) is


Conclusion.


Hence, the zero of the polynomial f(x) is




Let Us Work Out 7.3
Question 1.

By applying Remainder Theorem, let us calculate and write the remainder that I shall get in every cases, when x3 – 3x2 + 2x + 5 is divided by

x – 2


Answer:

Remainder theorem says that,


f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


Let us solve the following questions on the basis of this remainder theorem.


When x3 – 3x2 + 2x + 5 is divided by (x – 2).


Let f(x) = x3 – 3x2 + 2x + 5 …(1)


Now, let’s find out the zero of the linear polynomial, (x – 2).


To find zero,


x – 2 = 0


⇒ x = 2


This means that by remainder theorem, when x3 – 3x2 + 2x + 5 is divided by (x – 2), the remainder comes out to be f(2).


From equation (1), remainder can be calculated as,


Remainder = f(2)


⇒ Remainder = (2)3 – 3(2)2 + 2(2) + 5


⇒ Remainder = 8 – 12 + 4 + 5


⇒ Remainder = 5


∴ the required remainder = 5.



Question 2.

By applying Remainder Theorem, let us calculate and write the remainder that I shall get in every cases, when x3 – 3x2 + 2x + 5 is divided by

x + 2


Answer:

Remainder theorem says that,


f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


Let us solve the following questions on the basis of this remainder theorem.


When x3 – 3x2 + 2x + 5 is divided by (x + 2).


Let f(x) = x3 – 3x2 + 2x + 5 …(1)


Now, let’s find out the zero of the linear polynomial, (x + 2).


To find zero,


x + 2 = 0


⇒ x = -2


This means that by remainder theorem, when x3 – 3x2 + 2x + 5 is divided by (x + 2), the remainder comes out to be f(-2).


From equation (1), remainder can be calculated as,


Remainder = f(-2)


⇒ Remainder = (-2)3 – 3(-2)2 + 2(-2) + 5


⇒ Remainder = -8 – 12 – 4 + 5


⇒ Remainder = -19


∴ the required remainder = -19



Question 3.

By applying Remainder Theorem, let us calculate and write the remainder that I shall get in every cases, when x3 – 3x2 + 2x + 5 is divided by

2x – 1


Answer:

Remainder theorem says that,


f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


Let us solve the following questions on the basis of this remainder theorem.


When x3 – 3x2 + 2x + 5 is divided by (2x – 1).


Let f(x) = x3 – 3x2 + 2x + 5 …(1)


Now, let’s find out the zero of the linear polynomial, (2x – 1).


To find zero,


2x – 1 = 0


⇒ 2x = 1


⇒ x = 1/2


This means that by remainder theorem, when x3 – 3x2 + 2x + 5 is divided by (2x – 1), the remainder comes out to be f(1/2).


From equation (1), remainder can be calculated as,


Remainder = f( 1/2 )


⇒ Remainder


⇒ Remainder


⇒ Remainder = -19


∴ the required remainder = -19



Question 4.

By applying Remainder Theorem, let us calculate and write the remainder that I shall get in every cases, when x3 – 3x2 + 2x + 5 is divided by

2x + 1


Answer:

Remainder theorem says that,


f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


Let us solve the following questions on the basis of this remainder theorem.


When x3 – 3x2 + 2x + 5 is divided by (2x + 1).


Let f(x) = x3 – 3x2 + 2x + 5 …(1)


Now, let’s find out the zero of the linear polynomial, (2x + 1).


To find zero,


2x + 1 = 0


⇒ 2x = -1


⇒ x = -1/2


This means that by remainder theorem, when x3 – 3x2 + 2x + 5 is divided by (2x + 1), the remainder comes out to be f(-1/2).


From equation (1), remainder can be calculated as,


Remainder = f(-1/2)


⇒ Remainder


⇒ Remainder


⇒ Remainder


⇒ Remainder


⇒ Remainder


⇒ Remainder


∴ the required remainder = 25/8



Question 5.

By applying Remainder Theorem, let us calculate and write the remainders, that I shall get when the following polynomials are divided by (x – 1).

x3 – 6x2 + 13x + 60


Answer:

Remainder theorem says that,


f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


Let us solve the following questions on the basis of this remainder theorem.


Let f(x) = x3 – 6x2 + 13x + 60 …(1)


When x3 – 6x2 + 13x + 60 is divided by (x – 1).


Now, let’s find out the zero of the linear polynomial, (x – 1).


To find zero,


x – 1 = 0


⇒ x = 1


This means that by remainder theorem, when x3 – 6x2 + 13x + 60 is divided by (x – 1), the remainder comes out to be f(1).


From equation (1), remainder can be calculated as,


Remainder = f(1)


⇒ Remainder = (1)3 – 6(1)2 + 13(1) + 60


⇒ Remainder = 1 – 6 + 13 + 60


⇒ Remainder = -5 + 73


⇒ Remainder = 68


∴ the required remainder = 68



Question 6.

By applying Remainder Theorem, let us calculate and write the remainders, that I shall get when the following polynomials are divided by (x – 1).

x3 – 3x2 + 4x + 50


Answer:

Remainder theorem says that,


f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


Let us solve the following questions on the basis of this remainder theorem.


Let f(x) = x3 – 3x2 + 4x + 50 …(1)


When x3 – 3x2 + 4x + 50 is divided by (x – 1).


Now, let’s find out the zero of the linear polynomial, (x – 1).


To find zero,


x – 1 = 0


⇒ x = 1


This means that by remainder theorem, when x3 – 3x2 + 4x + 50 is divided by (x – 1), the remainder comes out to be f(1).


From equation (1), remainder can be calculated as,


Remainder = f(1)


⇒ Remainder = (1)3 – 3(1)2 + 4(1) + 50


⇒ Remainder = 1 – 3 + 4 + 50


⇒ Remainder = 1 + 1 + 50


⇒ Remainder = 52


∴ the required remainder = 52



Question 7.

By applying Remainder Theorem, let us calculate and write the remainders, that I shall get when the following polynomials are divided by (x – 1).

4x3 + 4x2 – x – 1


Answer:

Remainder theorem says that,


f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


Let us solve the following questions on the basis of this remainder theorem.


Let f(x) = 4x3 + 4x2 – x – 1 …(1)


When 4x3 + 4x2 – x – 1 is divided by (x – 1).


Now, let’s find out the zero of the linear polynomial, (x – 1).


To find zero,


x – 1 = 0


⇒ x = 1


This means that by remainder theorem, when 4x3 + 4x2 – x – 1 is divided by (x – 1), the remainder comes out to be f(1).


From equation (1), remainder can be calculated as,


Remainder = f(1)


⇒ Remainder = 4(1)3 + 4(1)2 – (1) – 1


⇒ Remainder = 4 + 4 – 1 – 1


⇒ Remainder = 8 – 2


⇒ Remainder = 6


∴ the required remainder = 6



Question 8.

By applying Remainder Theorem, let us calculate and write the remainders, that I shall get when the following polynomials are divided by (x – 1).

11x3 – 12x2 – x + 7


Answer:

Remainder theorem says that,


f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


Let us solve the following questions on the basis of this remainder theorem.


Let f(x) = 11x3 – 12x2 – x + 7 …(1)


When 11x3 – 12x2 – x + 7 is divided by (x – 1).


Now, let’s find out the zero of the linear polynomial, (x – 1).


To find zero,


x – 1 = 0


⇒ x = 1


This means that by remainder theorem, when 11x3 – 12x2 – x + 7 is divided by (x – 1), the remainder comes out to be f(1).


From equation (1), remainder can be calculated as,


Remainder = f(1)


⇒ Remainder = 11(1)3 – 12(1)2 – (1) + 7


⇒ Remainder = 11 – 12 – 1 + 7


⇒ Remainder = -1 – 1 + 7


⇒ Remainder = -2 + 7


⇒ Remainder = 5


∴ the required remainder = 5



Question 9.

Applying Remainder Theorem, let us write the remainders, when,

the polynomial x3 – 6x2 + 9x – 8 is divided by (x – 3)


Answer:

Remainder theorem says that,


f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


Let us solve the following questions on the basis of this remainder theorem.


Let f(x) = x3 – 6x2 + 9x – 8 …(1)


When x3 – 6x2 + 9x – 8 is divided by (x – 3).


Now, let’s find out the zero of the linear polynomial, (x – 3).


To find zero,


x – 3 = 0


⇒ x = 3


This means that by remainder theorem, when x3 – 6x2 + 9x – 8 is divided by (x – 3), the remainder comes out to be f(3).


From equation (1), remainder can be calculated as,


Remainder = f(3)


⇒ Remainder = (3)3 – 6(3)2 + 9(3) – 8


⇒ Remainder = 27 – 54 + 27 – 8


⇒ Remainder = -27 + 27 – 8


⇒ Remainder = 0 – 8


⇒ Remainder = -8


∴ the required remainder = -8



Question 10.

Applying Remainder Theorem, let us write the remainders, when,

the polynomial x3 – ax2 + 2x – a is divided by (x – a)


Answer:

Remainder theorem says that,


f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


Let us solve the following questions on the basis of this remainder theorem.


Let f(x) = x3 – ax2 + 2x – a …(1)


When x3 – ax2 + 2x – a is divided by (x – a).


Now, let’s find out the zero of the linear polynomial, (x – a).


To find zero,


x – a = 0


⇒ x = a


This means that by remainder theorem, when x3 – ax2 + 2x – a is divided by (x – a), the remainder comes out to be f(a).


From equation (1), remainder can be calculated as,


Remainder = f(a)


⇒ Remainder = (a)3 – a(a)2 + 2(a) – a


⇒ Remainder = a3 – a3 + 2a – a


⇒ Remainder = 2a – a


⇒ Remainder = a


∴ the required remainder = a



Question 11.

Applying Remainder Theorem, let us calculate whether the polynomial.

P(x) = 4x3 + 4x2 – x – 1 is a multiple of (2x + 1) or not.


Answer:

Remainder theorem says that,


f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


Let us solve the questions on the basis of this theorem.


Here, let f(x) = 4x3 + 4x2 – x – 1 …(i)


First, we need to find zero of the linear polynomial, (2x + 1).


To find zero,


2x + 1 = 0


⇒ 2x = -1


⇒ x = - 1/2


f(x) will be multiple of (2x + 1) if f(-1/2) = 0.






⇒ P(x) = 4x3 + 4x2 – x – 1 is a multiple of (2x + 1).



Question 12.

For what value of a, the divisions of two polynomials (ax3 + 3x2 – 3) and (2x3 – 5x + a) by (x – 4) give the same remainder —let us calculate and write it.


Answer:

Let the two polynomials be,


P(x) = ax3 + 3x2 – 3 …(i)


Q(x) = 2x3 – 5x + a …(ii)


Now, we understand by the question that,


P(x) and Q(x) divided by (x – 4) gives the same remainder.


We need to find zero of the linear polynomial, (x – 4).


To find zero, put (x – 4) = 0


⇒ x – 4 = 0


⇒ x = 4


By Remainder theorem that says, f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


Here, a = 4.


This means, remainder when P(x) is divided by (x – 4) is P(4).


⇒ Remainder = P(4)


⇒ Remainder = a(4)3 + 3(4)2 – 3


⇒ Remainder = 64a + 48 – 3


⇒ Remainder = 64a + 45 …(iii)


And remainder when Q(x) is divided by (x – 4) is Q(4).


⇒ Remainder = Q(4)


⇒ Remainder = 2(4)3 – 5(4) + a


⇒ Remainder = 128 – 20 + a


⇒ Remainder = 108 + a …(iv)


When P(x) and Q(x) are divided (x – 4) , they leave same remainder.


Comparing equations (iii) and (iv), we have


64a + 45 = 108 + a


⇒ 64a – a = 108 – 45


⇒ 63a = 63



⇒ a = 1


Thus, a = 1.



Question 13.

The two polynomials x3 + 2x2 – px – 7 and x3 + px2 – 12x + 6 are divided by (x + 1) and (x – 2) respectively and if the remainders R1 and R2 are obtained and if 2R1 + R2 = 6, then let us calculate the value of p.


Answer:

Let the polynomials be:


A(x) = x3 + 2x2 – px – 7


B(x) = x3 + px2 – 12x + 6


We will use remainder theorem here.


By Remainder theorem that says, f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


When A(x) is divided by (x + 1), it will leave remainder R1.


Let’s also find zero of linear polynomial, (x + 1).


To find zero,


⇒ x + 1 = 0


⇒ x = -1


The required remainder, R1 = A(-1).


⇒ R1 = (-1)3 + 2(-1)2 – p(-1) – 7


⇒ R1 = -1 + 2 + p – 7


⇒ R1 = 1 – 7 + p


⇒ R1 = p – 6 …(i)


When B(x) is divided by (x – 2), it will leave remainder R2.


Let’s also find zero of linear polynomial, (x – 2).


To find zero,


⇒ x – 2 = 0


⇒ x = 2


The required remainder, R2 = B(2)


⇒ R2 = (2)3 + p(2)2 – 12(2) + 6


⇒ R2 = 8 + 4p – 24 + 6


⇒ R2 = 4p + 14 – 24


⇒ R2 = 4p – 10 …(ii)


We have, 2R1 + R2 = 6


Substituting values from (i) and (ii), we get


2(p – 6) + (4p – 10) = 6


⇒ 2p – 12 + 4p – 10 = 6


⇒ 6p – 22 = 6


⇒ 6p = 6 + 22


⇒ 6p = 28




Thus, p = 14/3.



Question 14.

If the polynomial x4 – 2x3 + 3x2 – ax + b is divided by (x – 1) and (x + 1) and the remainders are 5 and 19 respectively. But if that polynomial is divided by x + 2, then what will be the remainder —Let us calculate.


Answer:

We have the polynomial x4 – 2x3 + 3x2 – ax + b.


Let it be P(x), such that


P(x) = x4 – 2x3 + 3x2 – ax + b …(i)


According to the question,


P(x) is divided by (x – 1) and (x + 1), and leaves the remainder 5 and 19 respectively.


We will use remainder theorem here.


By Remainder theorem that says, f(x) is a polynomial of degree n (n ≥ 1) and ‘a’ is any real number. If f(x) is divided by (x – a), then the remainder will be f(a).


At first, let’s find the zero of the linear polynomial, (x – 1).


To find zero,


x – 1 = 0


⇒ x = 1


Now, let’s find the zero of the linear polynomial, (x + 1).


To find zero,


x + 1 = 0


⇒ x = -1


From Remainder theorem, we can say


When P(x) is divided by (x – 1), the remainder comes out to be 5.


We can also say that,


The remainder comes out to be P(1).


⇒ P(1) = 5


⇒ (1)4 – 2(1)3 + 3(1)2 – a(1) + b = 5


⇒ 1 – 2 + 3 – a + b = 5


⇒ b – a + 2 = 5


⇒ b – a = 5 – 2


⇒ b – a = 3 …(ii)


And when P(x) is divided by (x + 1), the remainder comes out to be 19.


We can also say that,


The remainder comes out to be P(-1)


⇒ P(-1) = 19


⇒ (-1)4 – 2(-1)3 + 3(-1)2 – a(-1) + b = 5


⇒ 1 + 2 + 3 + a + b = 5


⇒ a + b + 6 = 5


⇒ a + b = 5 – 6


⇒ a + b = -1 …(iii)


Solving equations (ii) and (iii), we get


(b – a) + (a + b) = 3 + (-1)


⇒ 2b = 3 – 1


⇒ 2b = 2



⇒ b = 1


Putting b = 1 in equation (ii),


b – a = 3


⇒ 1 – a = 3


⇒ a = 1 – 3


⇒ a = -2


The values of a = -2 and b = 1.


∵ The polynomial = x4 – 2x3 + 3x2 – ax + b


∴ The polynomial = x4 – 2x3 + 3x2 – (-2)x + 1


⇒ The polynomial = x4 – 2x3 + 3x2 + 2x + 1


So, when polynomial x4 – 2x3 + 3x2 + 2x + 1 is divided by (x + 2), the remainder can be calculated by using Remainder theorem.


First, we need to find zero of the linear polynomial, (x + 2).


To find zero,


Put (x + 2) = 0


⇒ x = -2


So, Required remainder = P(-2)


⇒ Required remainder = (-2)4 – 2(-2)3 + 3(-2)2 + 2(-2) + 1


⇒ Required remainder = 16 + 16 + 12 – 4 + 1


⇒ Required remainder = 32 + 12 – 3


⇒ Required remainder = 44 – 3


⇒ Required remainder = 41


Thus, remainder is 41.



Question 15.

If then let us show that, f(a) + f(b) = f(a + b)


Answer:

We have



Let us simplify it,





⇒ f(x) = x …(i)


To show, f(a) + f(b) = f(a + b)


Take LHS: f(a) + f(b)


Just replace x by a in equation (i),


f(a) = a


Now, replace x by b in equation (i),


f(b) = b


LHS: f(a) + f(b)


⇒ f(a) + f(b) = a + b …(ii)


Now, Put (a + b) in equation (i),


f(a + b) = a + b


Replace (a + b) in equation (ii) from f(a + b), we get


f(a) + f(b) = f(a + b)


Thus, shown that f(a) + f(b) = f(a + b).



Question 16.

If f(x) = ax + b and f(0) = 3, f(2) = 5, then let us determine the values of a and b.


Answer:

We have,


f(x) = ax + b …(i)


f(0) = 3


f(2) = 5


Replace x by 0 in equation (i), we get


f(0) = a(0) + b


⇒ 3 = 0 + b [∵ f(0) = 3]


⇒ 3 = b


⇒ b = 3


Replace x by 2 in equation (i), we get


f(2) = a(2) + b


⇒ 5 = 2a + b [∵ f(2) = 5]


⇒ 5 = 2a + 3 [∵ b = 3]


⇒ 2a = 5 – 3


⇒ 2a = 2


⇒ a = 1


Thus, a = 1 and b = 3.



Question 17.

If f(x) = ax2 + bx + c and f(0) = 2, f(1) = 1 and f(4) = 6, then let us calculate the values of a, b and c.


Answer:

We have,


f(x) = ax2 + bx + c …(i)


f(0) = 2


f(1) = 1


f(4) = 6


Replace x by 0 in equation (i), we get


f(0) = a(0)2 + b(0) + c


⇒ 2 = 0 + 0 + c [∵ f(0) = 2]


⇒ 2 = c


⇒ c = 2 …(ii)


Now, replace x by 1 in equation (i), we get


f(1) = a(1)2 + b(1) + c


⇒ 1 = a + b + 2 [∵ f(1) = 1 & c = 2]


⇒ a + b = 1 – 2


⇒ a + b = -1 …(iii)


Finally, replace x by 4 in equation (i), we get


f(4) = a(4)2 + b(4) + c


⇒ 6 = 16a + 4b + 2 [∵ f(4) = 6 & c = 2]


⇒ 16a + 4b = 6 – 2


⇒ 16a + 4b = 4


⇒ 4 (4a + b) = 4


⇒ 4a + b = 1 …(iv)


Solving equations (iii) & (iv), we get



⇒ -3a = -2



Put a = 2/3 in equation (iii), we get






Thus, a = 2/3, b = -5/3 and c = 2.



Question 18.

Which of the followings is a polynomial in one variable?
A.

B.

C.

D. x10 + y5 + 8


Answer:

Let us check for the option (a),


We have


We can write it as, x + 2x-1 + 3.


Here, x-1 is a polynomial.


⇒ x + 2x-1 + 3 is not a polynomial.


is not a polynomial.


For option (b),


We have


We can write it as, 3√x + 2x-1/2 + 5.


Here, x- 1/2 is not a polynomial.


⇒ 3√x + 2x- 1/2 + 5 is not a polynomial.


is not a polynomial.


For option (c),


We have √2x2 - √3x + 6


Term-wise, √2 x2 is a polynomial


√3 x is a polynomial


6 is a polynomial


⇒ √2 x2 - √3 x + 6 is a polynomial.


For option (d),


We have x10 + y5 + 8.


Here, we have two variables, x and y.


Hence, it is clearly not a polynomial of single variable.


Thus, option (d) is correct.


Question 19.

Which of the following is a polynomial?
A. x – 1

B.

C.

D.


Answer:

For option (a),


We have x – 1


Look at each term individually, there’s no violation of the definition of polynomials.


The exponent in the algebraic expression is non-negative integers, that’s why we can say that (x – 1) is a polynomial.


For option (b),


We have


Rearranging the expression, we get



Even after re-arranging the expression, notice that the variable in both terms is appearing in denominator, which does not satisfy the definition of polynomials as variables cannot appear in denominator in the expression of a polynomial.


For option (c),


We have


Simplifying the expression, we get


x2 – 2x-2 + 5


Look at the term 2x-2.


In polynomials, the exponent in the algebraic expression should be non-negative integers, but in this expression the exponent is negative.


is not a polynomial.


For option (d),


We have


Simplifying the expression, we get






Observe the rational root in the second term of the expression, but in polynomials, the exponent should be non-negative integers.


is not a polynomial.


Thus, option (a) is correct.


Question 20.

Which of the followings is a linear polynomial?
A. x + x2

B. x + 1

C. 5x2 – x + 3

D.


Answer:

For option (a),


We have x + x2


In this expression, we have 2 terms.


The degree of this expression is 2 (largest exponent of x).


But linear polynomial has a degree of 1, so that it can give exactly one root.


⇒ x + x2 is not a linear polynomial.


For option (b),


We have x + 1


In this expression, we have 2 terms.


And the degree of this expression is 1 (largest exponent of x).


This compliments the definition of a polynomial.


⇒ x + 1 is a linear polynomial.


For option (c),


We have 5x2 – x + 3.


In this expression, we have 3 terms.


And the degree of this expression is 2 (largest exponent of x).


This violates the definition of linear polynomial, as the degree of linear polynomial is always 1.


⇒ 5x2 – x + 3 is not a linear polynomial.


For option (d),


We have


Let us simplify the expression.



⇒ x2 = 1


⇒ x2 – 1 = 0


This now is an algebraic expression, having 2 terms.


The degree of this expression is 2 (largest exponent of x).


This again doesn’t satisfy the criteria of linear polynomial, which says that degree should be 1.


is not a linear polynomial.


Thus, option (b) is correct.


Question 21.

Which of the followings is a second degree polynomial?
A.

B. x3 + x

C. x3 + 2x + 6

D. x2 + 5x + 6


Answer:

For option (a),


We have √x – 4.


Observe the two terms, x has an exponent of 1/2.


But for second degree polynomials, the degree should be 2 (that is, largest exponent of x should be 2)


⇒ √x – 4 is not a second degree polynomial.


For option (b),


We have x3 + x.


The degree of this expression is 3 (largest exponent of x is 3).


But for second degree polynomials, the degree should be 2 (that is, largest exponent of x should be 2)


⇒ x3 + x is not a second degree polynomial.


For option (c),


We have x3 + 2x + 6.


The degree of this expression is also 3 (largest exponent of x is 3).


But for second degree polynomials, the degree should be 2 (that is, largest exponent of x should be 2)


⇒ x3 + 2x + 6 is not a second degree polynomial.


For option (d),


We have x2 + 5x + 6.


The degree of this expression is 2 (largest exponent of x is 2).


This satisfies the criteria of second degree polynomial.


⇒ x2 + 5x + 6 is second degree polynomial.


Thus, option (d) is correct.


Question 22.

The degree of the polynomial is
A.

B. 2

C. 1

D. 0


Answer:

We have got polynomial, √3.


We can re-write it as, √3 x0 [∵ x0 = 1; any variable or number with exponent 0 gives 1 every time]


So, notice the exponent of x. Here, it is 0.


Since, degree of a term is sum of exponents of the variables that appears in it, and thus is a non-negative integer.


⇒ Degree of the polynomial = 0


Thus, option (d) is correct.


Question 23.

Let us write the zero of the polynomial p(x) = 2x –3.


Answer:

A zero is root of a polynomial function which is a number that, when plugged in for the variable, makes the function equal to zero.

To find the zero of a polynomial, just equate the polynomial equals to 0 and find out the value of the variable.


Here, p(x) = 0


⇒ 2x – 3 = 0


⇒ 2x = 3



Thus, zero of the polynomial is 3/2.



Question 24.

If p(x) = x + 4, let us write the value of p(x) + p(–x).


Answer:

We know,

p(x) = x + 4 …(i)


Now, to find p(-x), just replace x by –x in the above expression. Let us do it.


p(-x) = (-x) + 4


⇒ p(-x) = -x + 4 …(ii)


Now, add equations (i) and (ii), we get


p(x) + p(-x) = (x + 4) + (-x + 4)


⇒ p(x) + p(-x) = x + 4 – x + 4


⇒ p(x) + p(-x) = 8


Thus, the values of p(x) + p(-x) = 8



Question 25.

Let us write the remainder, if the polynomial x3 + 4x2 + 4x – 3 is divided by x.


Answer:

If the polynomial x3 + 4x2 + 4x – 3 is divided by x, we need to find the remainder.

Let P(x) = x3 + 4x2 + 4x – 3 …(i)


Next, we need to find the zero of the linear polynomial, x.


To find zero, equate x to 0.


⇒ x = 0


So, when P(x) is divided by x, it leaves a remainder P(0).


Replace x by 0 in equation (i), we get


P(0) = (0)3 + 4(0)2 + 4(0) – 3


⇒ P(0) = 0 + 0 + 0 – 3


⇒ P(0) = -3


⇒ Required remainder = -3


Thus, -3 is the answer.



Question 26.

If (3x – 1)7 = a7x7 + a6x6 + a5x5 + ………..+ a1x + a0, then let us write the value of a7 + a6 + a5 + …….. a0 (where a7, a6 ……………a0 are constants)


Answer:

We have been given that,

(3x – 1)7 = a7x7 + a6x6 + a5x5 + … + a1x + a0


If we simply put x = 1 in the above equation,


(3(1) – 1)7 = a7(1)7 + a6(1)6 + a5(1)5 + …+ a1(1) + a0


⇒ a7 + a6 + a5 + … + a1 + a0 = (3 – 1)7


⇒ a7 + a6 + a5 + … + a1 + a0 = 27


⇒ a7 + a6 + a5 + … + a1 + a0 = 128


Thus, value of a7 + a6 + a5 + … + a1 + a0 = 128.



Let Us Work Out 7.4
Question 1.

Let us calculate and write, which of the following polynomials will have a factor (x + 1)?

2x3 + 3x2 – 1


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial x + 1


x + 1 = 0


x = – 1


if f(x) is 2x3 + 3x2 – 1


then putting x = – 1;


f( – 1) = 2( – 1)3 + 3( – 1)2 – 1


= 2 × ( – 1) + 3 × (1) – 1


= – 2 + 3 – 1


= 0


Conclusion.


∴ (x + 1) is a factor of 2x3 + 3x2 – 1



Question 2.

Let us calculate and write, which of the following polynomials will have a factor (x + 1)?

x4 + x3 – x2 + 4x + 5


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial x + 1


x + 1 = 0


x = – 1


if f(x) is x4 + x3 – x2 + 4x + 5


then putting x = – 1;


f( – 1) = ( – 1)4 + ( – 1)3 – ( – 1)2 + 4( – 1) + 5


= 1 – 1 – 1 – 4 + 5


= 0


Conclusion.


∴ (x + 1) is a factor of x4 + x3 – x2 + 4x + 5



Question 3.

Let us calculate and write, which of the following polynomials will have a factor (x + 1)?

7x3 + x2 + 7x + 1


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial x + 1


x + 1 = 0


x = – 1


if f(x) is 7x3 + x2 + 7x + 1


then putting x = – 1;


f( – 1) = 7( – 1)3 + ( – 1)2 + 7( – 1) + 1


= 7 × ( – 1) + 1 + 7 × ( – 1) + 1


= – 7 + 1 – 7 + 1


= – 12


Conclusion.


∴ (x + 1) is not a factor of 7x3 + x2 + 7x + 1



Question 4.

Let us calculate and write, which of the following polynomials will have a factor (x + 1)?

3 + 3x – 5x3 – 5x4


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial x + 1


x + 1 = 0


x = – 1


if f(x) is 3 + 3x – 5x3 – 5x4


then putting x = – 1;


f( – 1) = 3 + 3( – 1) – 5( – 1)3 – 5( – 1)4


= 3 + 3 × ( – 1) – 5 × ( – 1) – 5 × 1


= 3 – 3 + 5 – 5


= 0


Conclusion.


∴ (x + 1) is a factor of 3 + 3x – 5x3 – 5x4



Question 5.

Let us calculate and write, which of the following polynomials will have a factor (x + 1)?

x4 + x2 + x + 1


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial x + 1


x + 1 = 0


x = – 1


if f(x) is x4 + x2 + x + 1


then putting x = – 1;


f( – 1) = ( – 1)4 + ( – 1)2 + ( – 1) + 1


= 1 + 1 – 1 + 1


= 2


Conclusion.


∴ (x + 1) is not a factor of x4 + x2 + x + 1



Question 6.

Let us calculate and write, which of the following polynomials will have a factor (x + 1)?

x3 + x2 + x + 1


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial x + 1


x + 1 = 0


x = – 1


if f(x) is x3 + x2 + x + 1


then putting x = – 1;


f( – 1) = ( – 1)3 + ( – 1)2 + ( – 1) + 1


= – 1 + 1 – 1 + 1


= 0


Conclusion.


∴ (x + 1) is a factor of x3 + x2 + x + 1



Question 7.

By using Factor Theorem, let us write whether g(x) is a factor of the following polynomials f(x).

f(x) = x4 – x2 and g(x) = x + 2


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial g(x)


x + 2 = 0


x = – 2


if f(x) is x4 – x2


then putting x = – 2 ;


f( – 2) = ( – 2)4 + ( – 2)2


= 16 + 4


= 20


Conclusion.


∴ g(x) is not a factor of f(x)



Question 8.

By using Factor Theorem, let us write whether g(x) is a factor of the following polynomials f(x).

f(x) = 2x3 + 9x2 – 11x – 30 and g(x) = x + 5


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial g(x)


x + 5 = 0


x = – 5


if f(x) is 2x3 + 9x2 – 11x – 30


then putting x = – 5 ;


f( – 5) = 2( – 5)3 + 9( – 5)2 – 11( – 5) – 30


= 2 × ( – 125) + 9 × (25) – 11x( – 5) – 30


= – 250 + 225 + 55 – 30


= 0


Conclusion.


∴ g(x) is a factor of f(x)



Question 9.

By using Factor Theorem, let us write whether g(x) is a factor of the following polynomials f(x).

f(x) = 2x3 + 7x2 – 24x – 45 and g(x) = x – 3


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial g(x)


x – 3 = 0


x = 3


if f(x) is 2x3 + 7x2 – 24x – 45


then putting x = 3 ;


f(3) = 2(3)3 + 7(3)2 – 24(3) – 45


= 2 × (27) + 7 × (9) – 24x(3) – 45


= 54 + 63 – 72 – 45


= 0


Conclusion.


∴ g(x) is a factor of f(x)



Question 10.

By using Factor Theorem, let us write whether g(x) is a factor of the following polynomials f(x).

f(x) = 3x3 + x2 – 20x + 12 and g(x) = 3x – 2


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial g(x)


3x – 2 = 0


x =


if f(x) is 3x3 + x2 – 20x + 12


then putting x = ;


f(3) = 3()3 + ()2 – 20() + 12


=


=


= = 0


Conclusion.


∴ g(x) is a factor of f(x)



Question 11.

Let us calculate and write the value of k for which the polynomial 2x4 + 3x3 + 2kx2 + 3x + 6 is divided by x + 2.


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial g(x)


x + 2 = 0


x = – 2


if x + 2 is factor of f(x) = 2x4 + 3x3 + 2kx2 + 3x + 6


then f( – 2) = 0 ;


f( – 2) = 2( – 2)4 + 3( – 2)3 + 2k( – 2)2 + 3( – 2) + 6 = 0


= 2 × 16 – 3 × 8 + 8 × k – 6 + 6


= 32 – 24 + 8k – 6 + 6


8 + 8k = 0


8k = – 8


k = = – 1


Conclusion.


∴ if (x + 2) is factor of f(x) then k = – 1



Question 12.

Let us calculate the value of k for which g(x) will be a factor of the following polynomials f(x).

f(x) = 2x3 + 9x2 + x + k and g(x) = x – 1


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial g(x)


x – 1 = 0


x = 1


if x – 1 is factor of f(x) = 2x3 + 9x2 + x + k


then f(1) = 0 ;


f(1) = 2(1)3 + 9(1)2 + 1 + k = 0


= 2 + 9 + 1 + k


12 + k = 0


k = – 12


Conclusion.


∴ if (x – 1) is factor of f(x) then k = – 12



Question 13.

Let us calculate the value of k for which g(x) will be a factor of the following polynomials f(x).

f(x) = kx2 – 3x + k and g(x) = x – 1


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial g(x)


x – 1 = 0


x = 1


if x – 1 is factor of f(x) = kx2 – 3x + k


then f(1) = 0 ;


f(1) = k(1)2 – 3(1) + k = 0


= k – 3 + k


2k – 3 = 0


k =


Conclusion.


∴ if (x – 1) is factor of f(x) then k = –



Question 14.

Let us calculate the value of k for which g(x) will be a factor of the following polynomials f(x).

f(x) = 2x4 + x3 – kx2 – x + 6 and g(x) = 2x – 3


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial g(x)


2x – 3 = 0


x =


if 2x – 3 is factor of f(x) = 2x4 + x3 – kx2 – x + 6


then f() = 0 ;


f() = 2()4 + 3 – k()2 + 6 = 0


=


=


=


= = 0


144 – 18k = 0


k = = 8


Conclusion.


∴ if (2x – 3) is factor of f(x) then k = 8



Question 15.

Let us calculate the value of k for which g(x) will be a factor of the following polynomials f(x).

f(x) = 2x3 + kx2 + 11x + k + 3 and g(x) = 2x – 1


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of polynomial g(x)


2x – 1 = 0


x =


if 2x – 1 is factor of f(x) = 2x3 + kx2 + 11x + k + 3


then f() = 0 ;


f() = 23 + k2 + 11() + k + 3 = 0


=


=


=


= = 0


70 + 10k = 0


k = = – 7


Conclusion.


∴ if (2x – 1) is factor of f(x) then k = – 7



Question 16.

Let us calculate and write the values of a and b if x2 – 4 is a factor of the polynomial ax4 + 2x3 – 3x2 + bx – 4.


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


⇒ a2 – b2 = (a + b)(a – b)


1st we find out zero of polynomial g(x)


x2 – 4 = 0


x2 – 22 = (x + 2)(x – 2) = 0


x + 2 = 0 and x – 2 = 0


x = – 2 and x = 2


if x + 2 is factor of f(x) = ax4 + 2x3 – 3x2 + bx – 4


then f( – 2) = 0 ;


f( – 2) = a( – 2)4 + 2( – 2)3 – 3( – 2)2 + b( – 2) – 4


= 16a – 16 – 12 – 2b – 4


16a – 2b – 32 = 0


16a = 32 + 2b ………eq 1


if x – 2 is factor of f(x) = ax4 + 2x3 – 3x2 + bx – 4


then f(2) = 0 ;


f(2) = a(2)4 + 2(2)3 – 3(2)2 + b(2) – 4


= 16a + 16 – 12 + 2b – 4


16a + 2b = 0 ………eq 2


Putting value of 16a from eq 1 into eq 2


(32 + 2b) + 2b = 0


32 + 4b = 0


4b = – 32


b = = – 8


Putting value of b in eq 1


16a = 32 + 2 × ( – 8)


16a = 32 – 16


16a = 16


a = = 1


Conclusion.


∴ if (x2 – 4) is factor of f(x) then b = – 8 and a = 1



Question 17.

If (x + 1) and (x + 2) are two factors of the polynomial x3 + 3x2 + 2ax + b, then let us calculate and write the values of a and b.


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


1st we find out zero of both polynomial (x + 1)(x + 2)


x + 1 = 0 and x + 2 = 0


x = – 1 and x = – 2


if x + 2 is factor of f(x) = x3 + 3x2 + 2ax + b


then f( – 2) = 0 ;


f( – 2) = ( – 2)3 + 3( – 2)2 + 2a( – 2) + b


= – 8 + 12 – 4a + b


b – 4a + 4 = 0


b = 4a – 4 ………eq 1


if x + 1 is factor of f(x) = x3 + 3x2 + 2ax + b


then f( – 1) = 0 ;


f( – 1) = ( – 1)3 + 3( – 1)2 + 2( – 1)a + b


= – 1 + 3 – 2a + b


b – 2a + 2 = 0 ………eq 2


Putting value of b from eq 1 into eq 2


(4a – 4) – 2a + 2 = 0


2a – 2 = 0


2a = 2


a = = 1


Putting value of a in eq 1


b = 4 × (1) – 4


= 0


Conclusion.


∴ if (x + 1) and (x + 2) is factor of f(x) then b = 0 and a = 1



Question 18.

If the polynomial ax3 + bx2 + x – 6 is divided by x – 2 and remainder is 4, then let us calculate the values of a and b when x + 2 is a factor of this polynomial.


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


⇒ Dividend = Divisor × Quotient + Remainder


When x + 2 is factor of polynomial


Then


x + 2 = 0


x = – 2


if x + 2 is factor of polynomial f(x) = ax3 + bx2 + x – 6


then f( – 2) is 0


f( – 2) = a( – 2)3 + b( – 2)2 + ( – 2) – 6 = 0


– 8a + 4b – 2 – 6 = 0


4b – 8a = 8


4b = 8 + 8a ……… eq 1


When x – 2 divides polynomial gives remainder 4


Then


Dividend = Divisor × Quotient + Remainder


ax3 + bx2 + x – 6 = (x – 2) × Quotient + 4


ax3 + bx2 + x – 6 – 4 = (x – 2) × Quotient


ax3 + bx2 + x – 10 = (x – 2) × Quotient


(x – 2) = 0


x = 2


if (x – 2) is factor of polynomial ax3 + bx2 + x – 10


then f(2) = 0


f(2) = a(2)3 + b(2)2 + 2 – 10


8a + 4b – 8 = 0


8a + 4b = 8 ………eq 2


Putting value of 4b from eq 1 into eq 2


8a + (8 + 8a) = 8


16a + 8 = 8


16a = 8 – 8 = 0


a = 0


Putting value of ‘a’ in eq 1


4b = 8 + 8a


4b = 8 + 8 × 0


4b = 8


b = = 2


Conclusion.


∴ The value of a and b comes to be 0 and 2 respectively



Question 19.

Let us show that if n is any positive integer (even or odd), x – y is a factor of the polynomial xn – yn.


Answer:

Formula used.


If f(x) is a polynomial with degree n


Then (x – a) is a factor of f(x) if f(a) = 0


⇒ Dividend = Divisor × Quotient + Remainder


If (x – y) is a factor of xn – yn


Then


We have to prove


On dividing xn – yn by (x – y) Remainder gets 0


When n = 1


(x – y) becomes factor of (x1 – y1)


Hence,


x – y = 0


x = y


Suppose on dividing xn – yn with x – y we get Remainder R


xn – yn = (x – y) × Quotient + R


Putting x = y


yn – yn = (y – y) × Quotient + R


0 = 0 + R


R = 0


∴ For every value n (x – y) is a factor of xn – yn


Conclusion.


⇒ For every value n (x – y) is a factor of xn – yn



Question 20.

Let us show that if n is any positive odd integer, then x + y is a factor of xn + yn.


Answer:

Let us suppose, if xn + yn is divided by x + y, the quotient is Q and remainder without x is R.


Dividend = Divisor × Quotient + Remainder


⸫ xn + yn = (x + y) × Q + R ……. [This is an identity]


Since x does not belong to the remainder R, the value of R will not change for any value of x.


So, in the above identity, putting (-y) for x, we get:


(-y)n + yn = (-y + y) × Q + R


Now, as n is odd, we get that (-y)n = - yn


so, we get,


- yn + yn = 0 × Q + R


0 = R


⸫ R = 0


⸫ (x + y) is a factor of the polynomial xn + yn, when n is an odd positive integer.



Question 21.

Let us show that if n be any positive integer (even or odd), the x – y never be a factor of the polynomial xn + yn.


Answer:

Let us suppose, if xn + yn is divided by x - y, the quotient is Q and remainder without x is R.


Dividend = Divisor × Quotient + Remainder


⸫ xn + yn = (x - y) × Q + R ……. [This is an identity]


Since x does not belong to the remainder R, the value of R will not change for any value of x.


So, in the above identity, putting (y) for x, we get:


(y)n + yn = (y - y) × Q + R


2(yn ) = 0 + R


2(yn ) = R


Since, value of R is not “0”, we can say that x – y is not a factor of the polynomial xn + yn


⸫ we can say that (x – y) can never be a factor of the polynomial xn + yn.



Question 22.

If the polynomial x3 + 6x2 + 4x + k is divisible by (x + 2), then the value of k is
A. –6

B. –7

C. –8

D. –10


Answer:

As it is given that, (x + 2) is a factor of the given polynomial, then -2 is the root of the polynomial.


So, as -2 is root of the polynomial and when we put -2 in the polynomial then it will give us “0” as the answer.


Now, we have,


(-2)3 + 6(-2)2 + 4(-2) + k = 0


-8 + 6×4 -8 + k = 0


-16 + 24 + k = 0


k + 8 = 0


k = -8


⸫ value of k is -8.


Hence, the correct option is (c).


Question 23.

In the polynomial f(x) if then the factor of f(x) will be
A. 2x – 1

B. 2x + 1

C. x – 1

D. x + 1


Answer:

In the question, it is given that which means that is a root of the polynomial f(x).


Which means that, [x – ()] =0 is a factor of the polynomial f(x).


[x + ()] =0 is a factor.


2x + 1 = 0 is a factor.


Hence the correct option is (b).


Question 24.

(x – 1) is a factor of the polynomial f(x) but it is not the factor of g(x). So (x – 1) will be a factor of
A. f(x) g(x)

B. –f(x) + g(x)

C. f(x) –g(x)

D. {f(x) + g(x)}g(x)


Answer:

We know that (x – 1) is a factor of the polynomial f(x) but it is not the factor of g(x).


Which means that, f(1) = 0 but g(1) ≠ 0.


But for (x - 1) to be a factor of the given options, when we put x=1 in the given functions we should get an answer as “0”.


So, for option (a), let F(x) = f(x) g(x)


To check whether (x – 1) is a factor of the polynomial F(x) we have to put x=1 in F(x) and see whether it gives us the answer as “0” or not.


F(1) = f(1) × g(1)


F(1) = 0 × g(1)


F(1) = 0


So, we can say that F(x) = f(x) g(x) is the polynomial whose factor is (x – 1).


⸫ (x – 1) will be the factor of f(x) g(x).


Hence the correct option is (a).


Question 25.

(x + 1) is a factor of the polynomial xn + 1 when
A. n is a positive odd integer

B. n is a positive even integer

C. n is a negative integer

D. n is a positive integer


Answer:

As we know that (x + y) is a factor of the polynomial xn + yn, when n is an odd positive integer, so here we can see that y = 1, so, we can say that (x + 1) is a factor of the polynomial xn + 1 when n is a positive odd integer.


Hence the correct option is (a).


Question 26.

If n2 – 1 is a factor of the polynomial an4 + bn3 + cn2 + dn + e then
A. a + c + e = b + d

B. a + b + e = c + d

C. a + b + c = d + e

D. b + c + d = a + e


Answer:

For the polynomial an4 + bn3 + cn2 + dn + e, we have n2 – 1 is a factor.


So, n2 – 1 = 0 is the root of the polynomial.


(n – 1)(n + 1) = 0


n = -1 or 1 are the roots of the given polynomial.


Now, when n = 1, we have:


a(1)4 + b(1)3 + c(1)2 + d(1) + e = 0


a + b + c + d + e = 0 ……... (1)


Now, when n = -1, we have:


a(-1)4 + b(-1)3 + c(-1)2 + d(-1) + e = 0


a – b + c – d + e = 0


a + c + e = d + b


Hence the correct option is (a).


Question 27.

Let us calculate and write the value of a for which x + a will be a factor of the polynomial x3 + ax2 – 2x + a – 12.


Answer:

We have the polynomial as x3 + ax2 – 2x + a – 12.


Given that x + a is the factor of the polynomial, which means that x = -a is the root of the polynomial.


So f(-a) = 0.


(-a)3 + a(-a)2 - 2(-a) + a – 12 = 0


-a3 + a3 + 2a + a – 12 = 0


3a – 12 = 0


3a = 12


a = 4.


⸫ value of a is 4.



Question 28.

Let us calculate and write the value of k for which x – 3 will be a factor of the polynomial k2x3 – kx2 + 3kx – k.


Answer:

We have the polynomial as k2x3 – kx2 + 3kx – k.


Given that x - 3 is the factor of the polynomial, which means that x = 3 is the root of the polynomial.


So f(3) = 0.


k2(3)3 – k(3)2 + 3k(3) – k = 0


27k2 – 9k + 9k – k = 0


27k2 – k = 0


k(27k – 1) = 0


k= 0 or


⸫ value of k is 0 or .



Question 29.

Let us write the value of f(x) + f(–x) when f(x) = 2x + 5.


Answer:

We have f(x) = 2x + 5


So, f(-x) = 2(-x) + 5


Now, f(x) + f(–x) = 2x + 5 + 2(-x) + 5


f(x) + f(–x) = 2x + 5 - 2x + 5


f(x) + f(–x) = 10.


⸫ value of f(x) + f(–x) when f(x) = 2x + 5 is 10.



Question 30.

Both (x – 2) and are factors of the polynomial px2 + 5x + r, let us calculate and write the relation between p and r.


Answer:

The given polynomial is px2 + 5x + r.


Given that, (x – 2) is the factor of the polynomial, we have f(2) = 0.


So, f(2) = p(2)2 + 5(2) + r = 0


4p + 10 + r = 0 ……… (1)


Now, given that, is the factor of the polynomial, we have


So,



From (1), we get r = -4p – 10


So, we can say that the relation between p and r is r = -4p – 10.


⸫ the relation between p and r is r = -4p – 10.



Question 31.

Let us write the zero of the linear polynomial f(x) = 2x + 3.


Answer:

The polynomial is f(x) = 2x + 3.


The zero of the polynomial means value of x for which f(x) = 0.


So, f(x) = 2x + 3 = 0


2x + 3 = 0


2x = -3



⸫ zero of the polynomial f(x) = 2x + 3 is .