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Factorisation Of Algebraic Expressions

Class 8th Mathematics West Bengal Board Solution
Lets Do 13.1
  1. x2 + 5x + 6 I/we factorise the following algebraic expressions:
  2. x2 + x – 6 I/we factorise the following algebraic expressions:
  3. x2 – x – 6 I/we factorise the following algebraic expressions:
  4. y2 + 23y + 102 I/we factorise the following algebraic expressions:…
  5. a2 + a – 132 I/we factorise the following algebraic expressions:
  6. p2 + 3p – 18 I/we factorise the following algebraic expressions:
Lets Work Out 13.1
  1. Comparing the following algebraic expression with the identity x2 + (p + q) x + pq= (x…
  2. (a + b)2-5a-5b + 6 Let’s resolve into factors
  3. (x2-2x)2 + 5(x2-2x)-36 Let’s resolve into factors
  4. (p2-3q2)2 - 16(p2-3q2) + 63 Let’s resolve into factors
  5. a4 + 4a2-5 Let’s resolve into factors
  6. x2y2 + 23xy-420 Let’s resolve into factors
  7. x4-7x2 + 12 Let’s resolve into factors
  8. a2 + ab-12b2 Let’s resolve into factors
  9. p2 + 31pq + 108q2 Let’s resolve into factors
  10. a6 + 3a3b3-40b6 Let’s resolve into factors
  11. (x + 1) (x + 3) (x-4) (x-6) + 24 Let’s resolve into factors
  12. Q2k (x + 1) (x + 9) (x + 5)2 + 63 Let’s resolve into factors
  13. x(x + 3)(x + 6)(x + 9) + 56 Let’s resolve into factors
  14. x2-2ax + (a + b)(a-b) Let’s resolve into factors
  15. x2-bx-(a + 3b)(a + 2b) Let’s resolve into factors
  16. (a + b)2-5a-5b + 6 Let’s resolve into factors
  17. x2 + 4abx-(a2-b2)2 Let’s resolve into factors
  18. x2- Let’s resolve into factors
  19. x6y6-9x3y3 + 8 Let’s resolve into factors
Lets Do 13.2
  1. Let's resolve into factors by expressing the algebraic expression (a2 – a – 72) and…
Lets Work Out 13.2
  1. 2a2 + 5a + 2 Let’s resolve into factors:
  2. 3x2 + 14x + 8 Let’s resolve into factors:
  3. 2m2 + 7m + 6 Let’s resolve into factors:
  4. 6x2-x-15 Let’s resolve into factors:
  5. 9r2 + r-8 Let’s resolve into factors:
  6. 6m2-11mn-10n2 Let’s resolve into factors:
  7. 7x2 + 48xy-7y2 Let’s resolve into factors:
  8. 12 + x-6x2 Let’s resolve into factors:
  9. 6 + 5a-6a2-45 Let’s resolve into factors:
  10. 6x2-13x + 6 Let’s resolve into factors:
  11. 99a2-202ab + 99b2 Let’s resolve into factors:
  12. 2a6-13a3-24 Let’s resolve into factors:
  13. 8a4 + 2a2-45 Let’s resolve into factors:
  14. 6(x-y)2-x + y-15 Let’s resolve into factors:
  15. 3(a + b)2-2a-2b-8 Let’s resolve into factors:
  16. 6(a + b)2 + 5(a2-b2)-6(a-b)2 Let’s resolve into factors:
  17. x2-2x-3 Let’s resolve the following algebraic expressions into factors by expressing…
  18. x2 + 5x + 6 Let’s resolve the following algebraic expressions into factors by…
  19. 3x2-7x-6 Let’s resolve the following algebraic expressions into factors by expressing…
  20. 3a2-2a-5 Let’s resolve the following algebraic expressions into factors by expressing…
  21. ax2 + (a2 + 1)x + a Let’s resolve into factors:
  22. x2 + 2ax + (a + b)(a-b) Let’s resolve into factors:
  23. ax2-(a2 + 1)x + a Let’s resolve into factors:
  24. ax2 + (a2-1)x-a Let’s resolve into factors:
  25. ax2-(a2-2)x-2a Let’s resolve into factors:
  26. a2 + 1- Let’s resolve into factors:

Lets Do 13.1
Question 1.

I/we factorise the following algebraic expressions:

x2 + 5x + 6


Answer:

An algebraic expression is an expression built up from integer constants, variables, and the algebraic operations.

And, factorization or factoring consists of writing a number or another mathematical object as a product of several factors, usually smaller or simpler objects of the same kind.


Let’s factorize the given algebraic expression.


We have x2 + 5x + 6.


First: Multiply the coefficient of x2 and the constant.


Coefficient of x2 = 1


Constant = 6


⇒ 1 × 6 = 6 …(a)


Now, Observe the coefficient of x = 5


We need to split the value obtained at (a), such that the sum\difference of the split numbers comes out to be 5.


To split: We need to find the factors of 6.


Factors of 6 = 2, 3


Add 2 and 3 = 2 + 3 = 5


Multiply 2 and 3 = 2 × 3 = 6


Since, the sum of 2 and 3 is 5 and multiplication is 6. So, we can write


x2 + 5x + 6 = x2 + (3x + 2x) + 6


⇒ x2 + 5x + 6 = x2 + 3x + 2x + 6


⇒ x2 + 5x + 6 = (x2 + 3x) + (2x + 6)


Now, take out common number or variable in first two pairs and the last two pairs subsequently.


⇒ x2 + 5x + 6 = x(x + 3) + 2(x + 3)


Now, take out the common number or variable again from the two pairs.


⇒ x2 + 5x + 6 = (x + 3)(x + 2)


Thus, the factorization of x2 + 5x + 6 = (x + 3)(x + 2).



Question 2.

I/we factorise the following algebraic expressions:

x2 + x – 6


Answer:

An algebraic expression is an expression built up from integer constants, variables, and the algebraic operations.

And, factorization or factoring consists of writing a number or another mathematical object as a product of several factors, usually smaller or simpler objects of the same kind.


Let’s factorize the given algebraic expression.


We have x2 + x – 6.


First: Multiply the coefficient of x2 and the constant.


Coefficient of x2 = 1


Constant = -6


⇒ 1 × -6 = -6 …(a)


Now, Observe the coefficient of x = 1


We need to split the value obtained at (a), such that the sum/difference of the split numbers comes out to be 1.


To split: We need to find the factors of -6.


Factors of -6 = 2, 3, -1


Add 3 and (2 × -1 =) -2 = 3 + (-2) = 1


Multiply 3 and -2 = 3 × -2 = -6


Since, the sum of -2 and 3 is 1 and multiplication is -6. So, we can write


x2 + x – 6 = x2 + (3x – 2x) – 6


⇒ x2 + x – 6 = x2 + 3x – 2x – 6


⇒ x2 + x – 6 = (x2 + 3x) + (-2x – 6)


Now, take out common number or variable in first two pairs and the last two pairs subsequently.


⇒ x2 + x – 6 = x(x + 3) – 2(x + 3)


Now, take out the common number or variable again from the two pairs.


⇒ x2 + x – 6 = (x + 3)(x – 2)


Thus, the factorization of x2 + x – 6 = (x + 3)(x – 2).



Question 3.

I/we factorise the following algebraic expressions:

x2 – x – 6


Answer:

An algebraic expression is an expression built up from integer constants, variables, and the algebraic operations.

And, factorization or factoring consists of writing a number or another mathematical object as a product of several factors, usually smaller or simpler objects of the same kind.


Let’s factorize the given algebraic expression.


We have x2 – x – 6.


First: Multiply the coefficient of x2 and the constant.


Coefficient of x2 = 1


Constant = -6


⇒ 1 × -6 = -6 …(a)


Now, Observe the coefficient of x = -1


We need to split the value obtained at (a), such that the sum/difference of the split numbers comes out to be -1.


To split: We need to find the factors of -6.


Factors of -6 = 2, 3, -1


Add (3 × -1 =) -3 and 2 = -3 + 2 = -1


Multiply -3 and 2 = -3 × 2 = -6


Since, the sum of 2 and -3 is 1 and multiplication is -6. So, we can write


x2 – x – 6 = x2 – (2x – 3x) – 6


⇒ x2 – x – 6 = x2 – 2x + 3x – 6


⇒ x2 – x – 6 = (x2 – 2x) + (3x – 6)


Now, take out common number or variable in first two pairs and the last two pairs subsequently.


⇒ x2 – x – 6 = x(x – 2) + 3(x – 2)


Now, take out the common number or variable again from the two pairs.


⇒ x2 – x – 6 = (x – 2)(x + 3)


Thus, the factorization of x2 – x – 6 = (x – 2)(x + 3).



Question 4.

I/we factorise the following algebraic expressions:

y2 + 23y + 102


Answer:

An algebraic expression is an expression built up from integer constants, variables, and the algebraic operations.

And, factorization or factoring consists of writing a number or another mathematical object as a product of several factors, usually smaller or simpler objects of the same kind.


Let’s factorize the given algebraic expression.


We have y2 + 23y + 102.


First: Multiply the coefficient of y2 and the constant.


Coefficient of y2 = 1


Constant = 102


⇒ 1 × 102 = 102 …(a)


Now, Observe the coefficient of y = 23


We need to split the value obtained at (a), such that the sum/difference of the split numbers comes out to be 23.


To split: We need to find the factors of 102.


Factors of 102 = 2 × 3 × 17


Add 17 and (2 × 3 =) 6 = 17 + 6 = 23


Multiply 17 and 6 = 17 × 6 = 102


Since, the sum of 17 and 6 is 23 and multiplication is 102. So, we can write


y2 + 23y + 102 = y2 + (17y + 6y) + 102


⇒ y2 + 23y + 102 = y2 + 17y + 6y + 102


⇒ y2 + 23y + 102 = (y2 + 17y) + (6y + 102)


Now, take out common number or variable in first two pairs and the last two pairs subsequently.


⇒ y2 + 23y + 102 = y(y + 17) + 6(y + 17)


Now, take out the common number or variable again from the two pairs.


⇒ y2 + 23y + 102 = (y + 17)(y + 6)


Thus, the factorization of y2 + 23y + 102 = (y + 17)(y + 6).



Question 5.

I/we factorise the following algebraic expressions:

a2 + a – 132


Answer:

An algebraic expression is an expression built up from integer constants, variables, and the algebraic operations.

And, factorization or factoring consists of writing a number or another mathematical object as a product of several factors, usually smaller or simpler objects of the same kind.


Let’s factorize the given algebraic expression.


We have a2 + a – 132.


First: Multiply the coefficient of a2 and the constant.


Coefficient of a2 = 1


Constant = -132


⇒ 1 × -132 = -132 …(a)


Now, Observe the coefficient of a = 1


We need to split the value obtained at (a), such that the sum/difference of the split numbers comes out to be 1.


To split: We need to find the factors of -132.


Factors of -132 = 2, 2, 3, 11, -1


Add (2 × 2 × 3 =) 12 and (11 × -1 =) -11 = 12 + (-11) = 1


Multiply 12 and -11 = 12 × -11 = -132


Since, the sum of 12 and -11 is 1 and multiplication is -132. So, we can write


a2 + a – 132 = a2 + (12a – 11a) – 132


⇒ a2 + a – 132 = a2 + 12a – 11a – 132


⇒ a2 + a – 132 = (a2 + 12a) + (-11a – 132)


Now, take out common number or variable in first two pairs and the last two pairs subsequently.


⇒ a2 + a – 132 = a(a + 12) – 11(a + 12)


Now, take out the common number or variable again from the two pairs.


⇒ a2 + a – 132 = (a + 12)(a – 11)


Thus, the factorization of a2 + a – 132 = (a + 12)(a – 11).



Question 6.

I/we factorise the following algebraic expressions:

p2 + 3p – 18


Answer:

An algebraic expression is an expression built up from integer constants, variables, and the algebraic operations.

And, factorization or factoring consists of writing a number or another mathematical object as a product of several factors, usually smaller or simpler objects of the same kind.


Let’s factorize the given algebraic expression.


We have p2 + 3p – 18.


First: Multiply the coefficient of p2 and the constant.


Coefficient of p2 = 1


Constant = -18


⇒ 1 × -18 = -18 …(a)


Now, Observe the coefficient of p = 3


We need to split the value obtained at (a), such that the sum/difference of the split numbers comes out to be 3.


To split: We need to find the factors of -18.


Factors of -18 = 2, 3, 3, -1


Add (2 × 3 =) 6 and (3 × -1 =) -3 = 6 + (-3) = 3


Multiply 6 and -3 = 6 × -3 = -18


Since, the sum of 6 and -3 is 3 and multiplication is -18. So, we can write


p2 + 3p – 18 = p2 + (6p – 3p) – 18


⇒ p2 + 3p – 18 = p2 + 6p – 3p – 18


⇒ p2 + 3p – 18 = (p2 + 6p) + (-3p – 18)


Now, take out common number or variable in first two pairs and the last two pairs subsequently.


⇒ p2 + 3p – 18 = p(p + 6) -3(p + 6)


Now, take out the common number or variable again from the two pairs.


⇒ p2 + 3p – 18 = (p + 6)(p – 3)


Thus, the factorization of p2 + 3p – 18 = (p + 6)(p – 3).




Lets Work Out 13.1
Question 1.

Comparing the following algebraic expression with the identity x2 + (p + q) x + pq= (x + p)(x + q), Let’s write the values of p and q and factorize them


(i) x2–40x–129 … (1)

(ii) m2 + 19m + 60 … (1)

(iii) x2-x-6 … (1)

(iv) (a + b)2 – 4(a + b) – 12 … (1)

(v) (x-y)2 – x + y – 2


Answer:

(i) To resolve it into factors, we first factorize 129


129= 3×43


Given, x2 + (p + q) x + pq


= (x + p)(x + q) … (2)


Comparing 1 and 2


p + q = - 40


= -43 + 3


pq = - 129


= -43 × 3


∴ (1) can be written as


x2-43x + 3x-129


x(x-43) + 3(x-43)


= (x-43) (x + 3)


∴ p=-43, q=3 and the resolved factors are (x-43) (x + 3).


(ii) To resolve it into factors, we first factorize 60


60=2×2×3×5


Given, x2 + (p + q) x + pq=(x + p)(x + q) … (2)


Comparing 1 and 2


p + q = 19


= 15 + 4


pq = 60


= 15× 4


∴ (1) can be written as


m2 + 15m + 4m + 60


= (m + 15) (m + 4)


∴ p=15, q=4 and the resolved factors are (m + 15) (m + 4).


(iii) To resolve it into factors, we first factorize 6


6= 3×2


Given, x2 + (p + q) x + pq=(x + p)(x + q) … (2)


Comparing 1 and 2


p + q = -1


= -3 + 2


pq =-6


= -3 × 2


∴ (1) can be written as


x2-3x + 2x-6


=(x-3)(x + 2)


∴ p=-3, q=2 and the resolved factors are (x-3)(x + 2).


(iv) to resolve it into factors we first resolve 12


12=2×2×3


Given, x2 + (p + q)x + pq=(x + p)(x + q) … (2)


Comparing 1 and 2


p + q = -4


= -6 + 2


pq =-12


= - 6 × 2


∴ (1) can be written as


(a + b)2 – 6(a + b) + 2(a + b)-12


=[{(a + b)-6}{(a + b) + 2}]


∴ p=-6, q=2 and the resolved factors are [{(a + b)-6} {(a + b) + 2}]


(v) (x-y)2 – x + y – 2


= (x-y)2 – (x-y) – 2 … (1)


To resolve it into factors, we first factorize 2


2= 1×2


Given, x2 + (p + q)x + pq=(x + p)(x + q) … (2)


Comparing 1 and 2


p + q = -1


= -2 + 1


pq = -2


= -2 × 1


∴ (1) can be written as


(x-y)2 – 2(x-y) + (x-y) – 2


= [{(x-y)-2}{(x-y) + 1}]


∴ p=-2, q=1 and the resolved factors are [{(x-y)-2}{(x-y) + 1}].



Question 2.

Let’s resolve into factors

(a + b)2-5a-5b + 6


Answer:

(a + b)2-5a-5b + 6


= (a + b)2-5(a + b) + 6 … (1)


To resolve it into factors we first resolve 6


6=2×3


We know, x2 + (p + q)x + pq=(x + p)(x + q) … (2)


Comparing 1 and 2


p + q = -5


= - 3 -2


pq = 6


= -3 × -2


∴ (1) can be written as


(a + b)2 – 3(a + b) - 2(a + b) + 6


(a + b) { a + b – 3} – 2 { a + b -3}


=[{a + b- 2}{a + b - 3}]


∴ the resolved factors are [{a + b- 2}{a + b - 3}]



Question 3.

Let’s resolve into factors

(x2-2x)2 + 5(x2-2x)-36


Answer:

(x2-2x)2 + 5(x2-2x)-36


To resolve it into factors we first resolve 36


36=9×4


We know, x2 + (p + q)x + pq=(x + p)(x + q) … (2)


Comparing 1 and 2 we get,


p + q = 5


= 9 -4


pq = - 36


= 9 × (-4)


∴ 1 can be written as:


(x2-2x)2 + 9(x2-2x) - 4(x2-2x) -36


= (x2-2x)[ (x2-2x) + 9] – 4 [(x2-2x) + 9]


= (x2-2x +9) (x2-2x - 4)



Question 4.

Let’s resolve into factors

(p2-3q2)2 - 16(p2-3q2) + 63


Answer:

To resolve it into factors we first resolve 63

63=7×3×3


Given, x2 + (m + n)x + mn=(x + m)(x + n) … (2)


Comparing 1 and 2


m + n = -16


mn =63


∴ (1) can be written as


(p2-3q2)2 - 9(p2-3q2) - 7(p2-3q2) + 63


=[{(p2-3q2) - 9}{(p2-3q2) - 7}]


∴ the resolved factors are [{(p2-3q2) - 9}{(p2-3q2) - 7}]



Question 5.

Let’s resolve into factors

a4 + 4a2-5


Answer:

(a2)2 + 4a2-5 … (1)

To resolve it into factors we first resolve 5


5=1×5


Given, x2 + (m + n)x + mn=(x + m)(x + n) … (2)


Comparing 1 and 2


m + n =4


mn =-5


∴ (1) can be written as


(a2)2 + 5a2- a2-5


= (a2 + 5)( a2-1)


∴ the resolved factors are (a2 + 5)( a2-1)



Question 6.

Let’s resolve into factors

x2y2 + 23xy-420


Answer:

To resolve it into factors, we first factorize 420

420= 2×2×3×5×7


Given, x2 + (p + q)x + pq=(x + p)(x + q) … (2)


Comparing 1 and 2


p + q = 23


pq =-420


∴ (1) can be written as


x2y2 + 35xy-12xy-420


= (xy + 35)(xy-12)


∴ The resolved factors are (xy + 35)(xy-12).



Question 7.

Let’s resolve into factors

x4-7x2 + 12


Answer:

(x2)2-7x2 + 12 … (1)

To resolve it into factors we first resolve 12


12=1×2×2×3


Given, x2 + (m + n)x + mn=(x + m)(x + n) … (2)


Comparing 1 and 2


m + n =-7


mn =12


∴ (1) can be written as


(x2)2-3x2-4x2 + 12


= x2(x2 – 3) – 4(x2 – 3)


= (x2-4)( x2-3)
We know a2 – b2 = (a – b)(a+b)


= (x-2)(x+2)( x2-3)


∴ The resolved factors are (x-2)(x+2)( x2-3)



Question 8.

Let’s resolve into factors

a2 + ab-12b2


Answer:

To resolve it into factors we first resolve 12

12=1×2×2×3


Given, x2 + (m + n)x + mn=(x + m)(x + n) … (2)


Comparing 1 and 2


m + n =1


mn =-12


∴ (1) can be written as


a2 + 4ab-3ab + 12b2


= (a + 4b)( a-3b)


∴ The resolved factors are (a + 4b)( a-3b).



Question 9.

Let’s resolve into factors

p2 + 31pq + 108q2


Answer:

To resolve it into factors we first resolve 108

108=2×2×3×3×3


Given, x2 + (m + n)x + mn=(x + m)(x + n) … (2)


Comparing 1 and 2


m + n =31


mn =108


∴ (1) can be written as


p2 + 27pq + 4pq + 108q2


= (p + 27q)( p + 4q)


∴ The resolved factors are (p + 27q)( p + 4q)



Question 10.

Let’s resolve into factors

a6 + 3a3b3-40b6


Answer:

(a3)2 + 3a3b3-40(b3)2

To resolve it into factors we first resolve 40


40=2×2×2×5


Given, x2 + (m + n)x + mn=(x + m)(x + n) … (2)


Comparing 1 and 2


m + n =3


mn =-40


∴ (1) can be written as


(a3)2 + 8a3b3-5a3b3-40(b3)2


= (a3 + 8b3)( a3-5b3)


∴ The resolved factors are (a3 + 8b3)( a3-5b3)


Apply the formula a3 + b3 = (a+b)(a2 + b2 – ab) in (a3 + 8b3)


Now (a3 + 8b3) = (a3 + (2b)3)


= (a2 + 4b2 – 2ab)( a3-5b3)


∴ The resolved factors are (a2 + 4b2 – 2ab)( a3-5b3).



Question 11.

Let’s resolve into factors

(x + 1) (x + 3) (x-4) (x-6) + 24


Answer:

= (x + 1)(x-4)(x + 3)(x-6) + 24


= (x2-4x + x-4)(x2–6x + 3x-18) + 24


= (x2-3x-4)(x2–3x-18) + 24


Let x2 – 3x = a


= (a-4)(a-18) + 24


= a2-18a-4a + 72 + 24


= a2-22a + 96


= a2-16a-6a + 96


= a(a-16)-6(a-16)


= (a-6)(a-16)


Putting back the values of a we get,


= (x2 – 3x -6)( x2 – 3x -16)



Question 12.

Let’s resolve into factors

(x + 1) (x + 9) (x + 5)2 + 63


Answer:

= (x2 + 9x + x + 9) (x + 5)2 + 63


Apply the formula (a + b)2 = a2 + b2 + 2ab in (x + 5)2


= (x2 + 10x + 9) (x2 + 10x + 25) + 63


Let x2 + 10x = a


= (a + 9)(a + 25) + 63


= a2 + 25a + 9a + 225 + 63


= a2 + 34a + 288


= a2 + 18a + 16a + 288


= a(a + 18) + 16(a + 18)


= (a + 16)(a + 18)


Putting back the values of a we get,


= (x2 + 10x + 16)( x2 + 10x + 18)


= (x2 + 8x + 2x + 16)(x2 + 10x + 18)


= [x(x + 8) + 2(x + 8)] (x2 + 10x + 18)


= (x + 8)(x + 2) (x2 + 10x + 18)



Question 13.

Let’s resolve into factors

x(x + 3)(x + 6)(x + 9) + 56


Answer:

x(x + 9)(x + 3)(x + 6) + 56


= (x2 + 9x) (x2 + 6x + 3x + 18) + 56


= (x2 + 9x) (x2 + 9x + 18) + 56


Let x2 + 9x = a


= a (a + 18) + 56


= a2 + 18a + 56


= a2 + 14a + 4a + 56


=a(a + 14) + 4(a + 14)


= (a + 4)(a + 14)


Put back the values to get,


= (x2 + 9x + 4)( x2 + 9x + 14)


= (x2 + 9x + 4)( x2 + 7x + 2x + 14)


= (x2 + 9x + 4)[( x(x + 7) + 2(x + 7)]


= (x2 + 9x + 4)(x + 2)(x + 7)



Question 14.

Let’s resolve into factors

x2-2ax + (a + b)(a-b)


Answer:

x2-2ax + (a + b)(a-b) … (1)

Given, x2 + (p + q)x + pq=(x + p)(x + q) … (2)


Comparing 1 and 2


p + q =-2a … (3)


pq =(a + b)(a-b) … (4)


to make the factors of 3 from 4


-2a=-(a-b)-(a + b)


∴ (1) can be written as


x2-(a-b)x-(a + b)x + (a + b)(a-b)


=[{x-(a-b)}{x-(a + b)}]


∴ the resolved factors are [{x-(a-b)}{x-(a + b)}]



Question 15.

Let’s resolve into factors

x2-bx-(a + 3b)(a + 2b)


Answer:

x2-bx-(a + 3b)(a + 2b) … (1)

Given, x2 + (p + q)x + pq=(x + p)(x + q) … (2)


Comparing 1 and 2


p + q =-b … (3)


pq =-(a + 3b)(a + 2b) … (4)


to make the factors of 3 from 4


-b= (a + 2b) – (a + 3b)


∴ (1) can be written as


x2 + (a + 2b)x – (a + 3b)x-(a + 3b)(a + 2b)


=[{x + (a + 2b)}{x-(a + 3b)}]


∴ the resolved factors are [{x + a + 2b)}{x- a - 3b)}]



Question 16.

Let’s resolve into factors

(a + b)2-5a-5b + 6


Answer:

(a + b)2-5(a + b) + 6 … (1)

To resolve it into factors we first resolve 6


6=2×3


Given, x2 + (p + q)x + pq=(x + p)(x + q) … (2)


Comparing 1 and 2


p + q = -5


pq =6


∴ (1) can be written as


(a + b)2 – 3(a + b) - 2(a + b) + 6


= (a+b)(a+b-3) -2(a+b-3)


=[{(a + b)-3}{(a + b) -2}]


∴ the resolved factors are [{(a + b)-6}{(a + b) + 1}]



Question 17.

Let’s resolve into factors

x2 + 4abx-(a2-b2)2


Answer:

x2 + 4abx-(a2-b2)2 … (1)

(a2-b2)2=[(a + b)2(a-b)2]2


Given, x2 + (p + q)x + pq=(x + p)(x + q) … (2)


Comparing 1 and 2


p + q = 4ab


pq =-(a2-b2)2


we know that (a + b)2=a2 + 2ab + b2 … (3)


similarly, (a-b)2=a2-2ab + b2 … (4)


subtracting 4 from 3


(a + b)2-(a-b)2 =a2 + 2ab + b2-( a2-2ab + b2)


=4ab


∴ (1) can be written as


x2 + (a + b)2x-(a-b)2x-[(a + b)2(a-b)2]2


=[{x + (a + b)2}{x-(a-b)2}]


Apply the formula (a+b)2 = a2 + b2 + 2ab


(a-b)2 = a2 + b2 - 2ab


=[{x + a2 + b2 + 2ab }{x-( a2 + b2 - 2ab )}]


=[{x + a2 + b2 + 2ab }{x- a2 - b2 + 2ab }]


∴ the resolved factors are [{x + a2 + b2 + 2ab }{x- a2 - b2 + 2ab }]



Question 18.

Let’s resolve into factors

x2-


Answer:







∴ the factors of are



Question 19.

Let’s resolve into factors

x6y6-9x3y3 + 8


Answer:

(x3y3)2-9x3y3 + 8 … (1)

To resolve it into factors we first resolve 8


8=2×2×2


Given, x2 + (m + n)x + mn=(x + m)(x + n) … (2)


Comparing 1 and 2


m + n =-9


mn =8


∴ (1) can be written as


(x3y3)2-8x3y3-x3y3 + 8


= (x3y3-8)( x3y3-1)


Apply the formula a3 - b3 = (a - b)(a2 + ab + b2) in (x3y3-8) and ( x3y3-1) as:


(x3y3-8) = ((xy)3 – 23)


= (xy-2) (x2y2 + 4 + 2xy)


(x3y3-1) = ((xy)3 – 13)


= (xy-1) (x2y2 + 1 + xy)


So,


(x3y3)2-8x3y3-x3y3 + 8 = (xy-2) (x2y2 + 4 + 2xy) (xy-1) (x2y2 + 1 + xy)


∴ the resolved factors are (xy-2) (x2y2 + 4 + 2xy) (xy-1) (x2y2 + 1 + xy)




Lets Do 13.2
Question 1.

Let's resolve into factors by expressing the algebraic expression (a2 – a – 72) and (2x2 – x – 1) as the difference of two squares.


Answer:

(a2 – a – 72)











= ( a – 9) (a + 8)


Now (2x2 – x – 1)


This can be written as:













Lets Work Out 13.2
Question 1.

Let’s resolve into factors:

2a2 + 5a + 2


Answer:

=2a2 + 4a + a + 2


=2a(a + 2) + 1(a + 2)


=(2a + 1)(a + 2)


∴ the factors of 2a2 + 5a + 2 are (2a + 1)(a + 2)



Question 2.

Let’s resolve into factors:

3x2 + 14x + 8


Answer:

3x2 + 14x + 8

=3x2 + 12x + 2x + 8


=3x(x + 4) + 2(x + 4)


=(3x + 2)(x + 4)


∴ the factors of 3x2 + 14x + 8 are (3x + 2)(x + 4)



Question 3.

Let’s resolve into factors:

2m2 + 7m + 6


Answer:

2m2 + 7m + 6

=2m2 + 4m + 3m + 6


=2m(m + 2) + 3(m + 2)


=(2m + 3)(m + 2)


∴ the factors of 2m2 + 7m + 6 are (2m + 3)(m + 2)



Question 4.

Let’s resolve into factors:

6x2-x-15


Answer:

6x2-x-15

=6x2-10x + 9x-15


=2x(3x-5) + 3(3x-5)


=(2x + 3)(3x-5)


∴ the factors of 6x2-x-15 are (2x + 3)(3x-5)



Question 5.

Let’s resolve into factors:

9r2 + r-8


Answer:

9r2 + r-8

=9r2 + 9r-8r-8


=9r(r + 1)-8(r + 1)


=(9r-8)(r + 1)


∴ the factors of 9r2 + r-8 are (9r-8)(r + 1)



Question 6.

Let’s resolve into factors:

6m2-11mn-10n2


Answer:

6m2-11mn-10n2

=6m2-15mn + 4mn-10n2


=3m(2m-5n) + 2n(3m-5n)


=(3m + 2n)(2m-5n)


∴ the factors of 6m2-11mn-10n2 are (3m + 2n)(2m-5n)



Question 7.

Let’s resolve into factors:

7x2 + 48xy-7y2


Answer:

7x2 + 48xy-7y2


=7x2 + 49xy-xy-7y2


=7x(x + 7y)-y(x + 7y)


=(7x-y)(x + 7y)


∴ the factors of 7x2 + 48xy-7y2 are (7x-y)(x + 7y)



Question 8.

Let’s resolve into factors:

12 + x-6x2


Answer:

12 + x-6x2


=-(6x2-x-12)


=-(6x2-9x + 8x-12)


=-{3x(2x-3) + 4(2x-3)}


=-(3x + 4)(2x-3)


= (3x + 4)(3-2x)


∴ the factors of 12 + x-6x2 are (3x + 4)(3-2x)



Question 9.

Let’s resolve into factors:

6 + 5a-6a2-45


Answer:

=-(6a2-5a-6)
= - (6a2-9a + 4a-6)


= - [3a(2a-3) + 2(2a-3)]


= - (3a + 2)(2a-3)


= (3a + 2)(3-2a)


∴ The factors of 6 + 5a-6a2 is (3a + 2)(3-2a).



Question 10.

Let’s resolve into factors:

6x2-13x + 6


Answer:

6x2-13x + 6

=6x2-9x-4x + 6


=3x(2x-3)-2(2x-3)


=(3x-2)(2x-3)


∴ the factors of 6x2-13x + 6 are (3x-2)(2x-3)



Question 11.

Let’s resolve into factors:

99a2-202ab + 99b2


Answer:

99a2-202ab + 99b2

=99a2-121ab-81ab + 99b2


=11a(9a-11b)-9b(9a-11b)


=(11a-9b)(9a-11b)


∴the factors of 99a2-202ab + 99b2 are (11a-9b)(9a-11b)



Question 12.

Let’s resolve into factors:

2a6-13a3-24


Answer:

2a6-13a3-24

=2a6-16a3 + 3a3-24


=2a3(a3-8) + 3(a3-8)


= (2a3 + 3) (a3-8)


Apply the formula a3 - b3 = (a - b)(a2 + ab + b2) in (a3-8),


(a3-8) = (a3-23)


= (a-2)(a2 + 4 + 2a)


So,


2a6-13a3-24= (2a3 + 3) (a-2)(a2 + 4 + 2a)


∴ the factors of 2a6-13a3-24 are (2a3 + 3) (a-2)(a2 + 4 + 2a).



Question 13.

Let’s resolve into factors:

8a4 + 2a2-45


Answer:

8a4 + 2a2-45


=8a4 + 20a2- 18a2-45


=4a2(2a2 + 5)-9(2a2 + 5)


=(4a2-9)(2a2 + 5)


Apply the formula a2 – b2 = (a-b) (a+b) in(4a2-9)


(4a2-9)= ((2a)2 – 32)


= (2a-3)(2a+3)


So,


8a4 + 2a2-45 = (2a2 + 5) (2a-3)(2a+3)


∴ the factors of 8a4 + 2a2-45 are (2a2 + 5) (2a-3)(2a+3)



Question 14.

Let’s resolve into factors:

6(x-y)2-x + y-15


Answer:

6(x-y)2-x + y-15


=6(x-y)2-(x-y)-15


=6(x-y)2-10(x-y) + 9(x-y)-15


=2(x-y){3(x-y)-5} + 3{3(x-y)-5}


=[{2(x-y) + 3}{3(x-y)-5}]


=[2x-2y+3][3x-3y-5]


∴ the factors of 6(x-y)2-x + y-15 are [2x-2y+3][3x-3y-5]



Question 15.

Let’s resolve into factors:

3(a + b)2-2a-2b-8


Answer:

3(a + b)2-2a-2b-8


=3(a + b)2-2(a + b)-8


=3(a + b)2-6(a + b) + 4(a + b)-8


=3(a + b){a + b-2} + 4(a + b-2)


=(3a + 3b + 4)(a + b-2)


∴ the factors of 3(a + b)2-2a-2b-8 are (3a + 3b + 4)(a + b-2)



Question 16.

Let’s resolve into factors:

6(a + b)2 + 5(a2-b2)-6(a-b)2


Answer:

6(a + b)2 + 5(a2-b2)-6(a-b)2


=6(a + b)2 + 5(a-b)(a + b)-6(a-b)2


=6(a + b)2 + 9(a-b)(a + b)-4(a-b)(a + b)-6(a-b)2


=3(a + b){2a + 2b + 3a-3b}-2(a-b){2a + 2b + 3a-3b}


=3(a + b)(5a-b)-2(a-b)(5a-b)


=(5a-b)(3a + 3b-2a + 3b)


=(5a-b)(a + 5b)


∴ the factors of 6(a + b)2 + 5(a2-b2)-6(a-b)2 are (5a-b)(a + 5b)



Question 17.

Let’s resolve the following algebraic expressions into factors by expressing them as the difference of two squares:

x2-2x-3


Answer:

Add and subtract the half of square of coefficient of x.




=(x-1)2 – 4


=(x-1)2 – (2)2


Apply the formula a2 – b2 = (a + b)(a-b)


= (x-1-2)(x-1 + 2)


= (x-3)(x + 1)


Hence the factors of x2-2x-3 are (x-3)(x + 1).



Question 18.

Let’s resolve the following algebraic expressions into factors by expressing them as the difference of two squares:

x2 + 5x + 6


Answer:

Add and subtract the half of square of coefficient of x.







Apply the formula a2 – b2 = (a + b)(a-b)





= (x + 2)(x + 3)


Hence the factors of x2 + 5x + 6 is (x + 2)(x + 3).



Question 19.

Let’s resolve the following algebraic expressions into factors by expressing them as the difference of two squares:

3x2-7x-6


Answer:

make the coefficient of x2 as 1.



Add and subtract the half of square of coefficient of x.







Apply the formula a2 – b2 = (a + b)(a-b)






= (x-3)(3x + 2)


Hence the factors of 3x2-7x-6 are (x-3)(3x + 2).



Question 20.

Let’s resolve the following algebraic expressions into factors by expressing them as the difference of two squares:

3a2-2a-5


Answer:

make the coefficient of a2 as 1.



Add and subtract the half of square of coefficient of “a”.







Apply the formula a2 – b2 = (a + b)(a-b)






= (3a-5)(a + 1)


Hence the factors of 3a2-2a-5 are (3a-5)(a + 1).



Question 21.

Let’s resolve into factors:

ax2 + (a2 + 1)x + a


Answer:

ax2 + (a2 + 1)x + a


=ax2 + a2x + x + a


=ax(x + a) + 1(x + a)


=(ax + 1)(x + a)


∴ the factors of ax2 + (a2 + 1)x + a are (ax + 1)(x + a)



Question 22.

Let’s resolve into factors:

x2 + 2ax + (a + b)(a-b)


Answer:

x2 + 2ax + (a + b)(a-b)

=x2 + (a + b)x + (a-b)x + (a + b)(a-b)


=x(x + a + b) + (a-b)(x + a + b)


=(x + a-b)(x + a + b)


∴ the factors of x2 + 2ax + (a + b)(a-b) are (x + a-b)(x + a + b)



Question 23.

Let’s resolve into factors:

ax2-(a2 + 1)x + a


Answer:

ax2-(a2 + 1)x + a


=ax2-a2x-x + a


=ax(x-a)-1(x-a)


=(ax-1)(x-a)


∴ the factors of ax2-(a2 + 1)x + a are (ax-1)(x-a)



Question 24.

Let’s resolve into factors:

ax2 + (a2-1)x-a


Answer:

ax2 + (a2-1)x-a


=ax2 + a2x-x-a


=ax(x + a)-1(x + a)


=(ax-1)(x + a)


∴ the factors of ax2 + (a2-1)x-a are (ax-1)(x + a)



Question 25.

Let’s resolve into factors:

ax2-(a2-2)x-2a


Answer:

ax2-(a2-2)x-2a

=ax2-a2x + 2x-2a


=ax(x-a) + 2(x-a)


=(ax + 2)(x-a)


∴ the factors of ax2-(a2-2)x-2a are (ax + 2)(x-a)



Question 26.

Let’s resolve into factors:

a2 + 1-


Answer:








∴ the factors of