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Factorisation Of Algebraic Expressions

Class 8th Mathematics (new) MHB Solution
Practice Set 6.1
  1. Factorise.x2 + 9x + 18
  2. Factorise.x2 – 10x + 9
  3. Factorise.y2 + 24y + 144
  4. Factorise.5y2 + 5y – 10
  5. Factorise.p2 – 2p – 35
  6. Factorise.p2 – 7p – 44
  7. Factorise.m2 – 23m + 120
  8. Factorise.m2 – 25m + 100
  9. Factorise.3x2 + 14x + 15
  10. Factorise.2x2 + x – 45
  11. Factorise.20x2 – 26x + 8
  12. Factorise.44x2 – x – 3
Practice Set 6.2
  1. Factorise.x3 + 64y3
  2. Factorise.125p3 + q3
  3. Factorise.125k3 + 27m3
  4. Factorise.2l3 + 432m3
  5. Factorise.24a3 + 81b3
  6. Factorise. y^{3} + {1}/{ 8y^{3} }
  7. Factorise. a^{3} + {8}/{ a^{3} }
  8. Factorise. 1 + { q^{3} }/{125}
Practice Set 6.3
  1. Factorise :y3 – 27
  2. Factorise :x3 – 64y3
  3. Factorise :27m3 – 216n3
  4. Factorise :125y3 – 1
  5. Factorise :8p3 – 27/p3
  6. Factorise :343a3 – 512b3
  7. Factorise :64x2 – 729y2
  8. Factorise :16 a3 – 128/b3
  9. Simplify :(x + y)3 – (x – y)3
  10. Simplify :(3a + 5b)3 – (3a – 5b)3
  11. Simplify :(a + b)3 – a3 – b3
  12. Simplify :p3 – (p + 1)3
  13. Simplify :(3xy – 2ab)3 – (3xy + 2ab)3
Practice Set 6.4
  1. Simplify: { m^{2} - n^{2} }/{ (m+11) } x frac { m^{2} + mn+n^{2} }/{ m^{3} - n^{3}…
  2. Simplify: { a^{2} + 10a+21 }/{ a^{2} + 6a-7 } x frac { a^{2} - 1 }/{a+3}…
  3. Simplify: { 8x^{3} - 27y^{3} }/{ 4x^{2} - 9y^{2} }
  4. Simplify: { x^{2} - 5x-24 }/{ (x+3) (x+8) } x frac { x^{2} - 64 }/{ (x-8)^{2} }…
  5. Simplify: { 3x^{2} - x-2 }/{ x^{2} - 7x+12 } / frac { 3x^{2} - 7x-6 }/{ x^{2} -…
  6. Simplify: { 4x^{2} - 11x+6 }/{ 16x^{2} - 9 }
  7. Simplify: { a^{3} - 27 }/{ 5a^{2} - 16a+3 } / frac { a^{2} + 3a+9 }/{ 25a^{2} -…
  8. Simplify: { 1-2x+x^{2} }/{ 1-x^{3} } x frac { 1+x+x^{2} }/{1+x}…

Practice Set 6.1
Question 1.

Factorise.

x2 + 9x + 18


Answer:

On comparing with standard quadratic equation that is

we have,


a = 1, b = 9 and c = 18


Now here,


Product ac = 118 = 18


Factors of 18; 29 and 63


Sum should be b = + 9


From above factors (+ 6x + 3x)


will give + 9x sum


therefore + 9x is replaced by ( + 6x + 3x)


Now above eq. becomes


x2 + 6x + 3x + 18


; taking x common


⇒ (x + 3)(x + 6)



Question 2.

Factorise.

x2 – 10x + 9


Answer:

On comparing with standard quadratic equation that is

we have,0


a = 1, b = – 10 and c = 9


Now here,


Product ac = 19 = 9


Factors of 9; 19 and 33


Sum should be b = – 10


From above factors ( – 1x – 9x)


will give – 10x sum


therefore – 10x is replaced by ( – 1x – 9x)


Now above eq. becomes



; taking x and – 9 common


(x – 1)(x – 9)



Question 3.

Factorise.

y2 + 24y + 144


Answer:

On comparing with standard quadratic equation that is

we have,


a = 1, b = + 24 and c = + 144


Now here,


Product a × c = 1 × 144 = 144


Factors of 144; 12 × 12; 24 × 6;144 × 1;


48 × 3; 72 × 2


Sum should be b = 24


From above factors (12y + 12y)


will give + 24y sum


therefore + 24 is replaced by ( + 12y + 12y)


Now above eq. becomes




; taking y and + 12 common


(y + 1)(y + 12)


Note: Try to find all factors of “c”, then choose from it that combination whose sum or difference give “b”



Question 4.

Factorise.

5y2 + 5y – 10


Answer:

On comparing with standard quadratic equation that is

we have,


a = 5, b = + 5 and c = – 10


Now here,


Product a × c = 5 × – 10 = – 50


Factors of 50; 5 × 10; 25 × 2;50 × 1


Sum should be b = + 5


From above factors ( – 5y + 10y)


will give + 5y sum


therefore + 5y is replaced by ( – 5y + 10y)


Now above eq. becomes



; taking 5y and + 10 common


(y – 1)(5y + 10)


5(y – 1)(y + 2); 5 common


Note: if given equation’s constant a,b,c have common multiple take it out and then factorize.



Question 5.

Factorise.

p2 – 2p – 35


Answer:

On comparing with standard quadratic equation that is

we have,


a = 1, b = – 2 and c = – 35


Now here,


Product a × c = 1 × – 35 = – 35


Factors of 35; 1 × 35 and 7 × 5


Sum should be b = – 2


From above factors ( – 7p + 5p)


will give – 2p sum


therefore – 2p is replaced by ( – 7p + 5p)


Now above eq. becomes



; taking p and + 5 common


(p – 7)(p + 5)



Question 6.

Factorise.

p2 – 7p – 44


Answer:

On comparing with standard quadratic equation that is

we have,


a = 1, b = – 7 and c = – 44


Now here,


Product a × c = 1 × – 44 = – 44


Factors of 44; 1 × 44; 2 × 22;4 × 11


Sum should be b = – 7


From above factors ( – 11p + 4p)


will give – 7p sum


therefore – 7p is replaced by ( – 11p + 4p)


Now above eq. becomes



; taking p and + 4 common


(p + 4)(p – 11)



Question 7.

Factorise.

m2 – 23m + 120


Answer:

On comparing with standard quadratic equation that is

a


we have,


a = 1, b = – 23 and c = + 120


Now here,


Product a × c = 1 × + 120 = + 120


Factors of + 120; 1 × 120; 2 × 60; 4 × 30; 8 × 15; 24 × 5; 40 × 3


Sum should be b = – 23


From above factors ( – 15m – 8m)


will give – 23m sum


therefore – 23m is replaced by ( – 15m – 8m)


Now above eq. becomes



; taking m and – 8 common


(m – 15)(m – 8)



Question 8.

Factorise.

m2 – 25m + 100


Answer:

On comparing with standard quadratic equation that is

we have,


a = 1, b = – 25 and c = 100


Now here,


Product a × c = 1 × 100 = 100


Factors of 100; 1 × 100; 2 × 50; 4 × 25;20 × 5


Sum should be b = – 25


From above factors ( – 20m – 5m)


will give – 25m sum


therefore – 25m is replaced by ( – 20m – 5m)


Now above eq. becomes



; taking m and – 5 common


(m – 5)(m – 20)



Question 9.

Factorise.

3x2 + 14x + 15


Answer:

On comparing with standard quadratic equation that is

we have,


a = 3, b = + 14 and c = + 15


Now here,


Product a × c = 3 × 15 = + 45


Factors of 45; 1 × 45; 5 × 9;15 × 3


Sum should be b = + 14


From above factors ( + 9x + 5x)


will give + 14x sum


therefore + 14x is replaced by ( + 9x + 5x)


Now above eq. becomes



; taking x and + 5 common


(x + 9)(x + 3)



Question 10.

Factorise.

2x2 + x – 45


Answer:

On comparing with standard quadratic equation that is

we have,


a = 2, b = 1 and c = – 45


Now here,


Product a × c = 2 × – 45 = 90


Factors of 90; 1 × 90; 2 × 45; 10 × 9; 30 × 3


Sum should be b = 1


From above factors ( + 10x – 9x)


will give + x sum


therefore + x is replaced by ( + 10x – 9x)


Now above eq. becomes



; taking 2x and – 9 common


(x + 5)(2x – 9)



Question 11.

Factorise.

20x2 – 26x + 8


Answer:

On comparing with standard quadratic equation that is

we have,


a = 20, b = – 26 and c = 8


Now here,


Product a × c = 20 × 8 = 160


Factors of 160; 2 × 80; 4 × 40; 8 × 20; 16 × 10; 32 × 5


Sum should be b = – 26x


From above factors ( – 16x – 10x)


will give – 26x sum


therefore – 26x is replaced by ( – 16x – 10x)


Now above eq. becomes



; taking 4x and – 2 common


2(2x – 1)(5x – 4)



Question 12.

Factorise.

44x2 – x – 3


Answer:

On comparing with standard quadratic equation that is

we have,


a = 44, b = – 1 and c = – 3


Now here,


Product a × c = – 132 = 44 × – 3


Factors of 132; 1 × 132; 2 × 66; 4 × 33;12 × 11


Sum should be b = – 1


From above factors ( – 12x – 11x)


will give – 1x sum


therefore – 1x is replaced by ( – 12x – 11x)


Now above eq. becomes



; taking x and – 9 common


(11x – 3)(4x – 1)




Practice Set 6.2
Question 1.

Factorise.

x3 + 64y3


Answer:

We know that


- - - - - (i)


Here a = 1x, b = 4y; putting values in eq.i







}


Note: Must memorize cubes upto 12



Question 2.

Factorise.

125p3 + q3


Answer:

We know that


- - - - - (i)


Here a = 5p, b = q; putting values in eq.i






}


Note: Must memorize cubes upto 12



Question 3.

Factorise.

125k3 + 27m3


Answer:

We know that


- - - - - (i)


Here a = 5k, b = 3m; putting values in eq.i




}


}


}


Note: Must memorize cubes upto 12



Question 4.

Factorise.

2l3 + 432m3


Answer:

We know that


- - - - - (i)


Taking 2 common, we get



Here a = l, b = 6m; putting values in eq.i




}]


}


Applying


}


Note: Must memorize cubes upto 12



Question 5.

Factorise.

24a3 + 81b3


Answer:

We know that


- - - - - (i)


Taking 3 as common, we get


3; solving only bracket term first,


Here a = 2a, b = 3b; putting values in eq.i




}


Applying


}


}


Ans: - 3}


Note: Must memorize cubes upto 12



Question 6.

Factorise.



Answer:

We know that


- - - - - (i)


Here a = y, b = ; putting values in eq.i






Applying



}


Note: Must memorize cubes upto 12



Question 7.

Factorise.



Answer:

We know that


- - - - - (i)


Here a = a, b = ; putting values in eq.i






Applying


}


}


Note: Must memorize cubes upto 12



Question 8.

Factorise.



Answer:

We know that


- - - - - (i)


Here a = 1, b = ; putting values in eq.i






Applying



}


Note: Must memorize cubes upto 12




Practice Set 6.3
Question 1.

Factorise :

y3 – 27


Answer:

We know that


on comparison with above, we get


a = y, b = 3



Note: Must memorize cubes upto 12



Question 2.

Factorise :

x3 – 64y3


Answer:

We know that


on comparison with above, we get


a = y, b = 3



Note: Must memorize cubes upto 12



Question 3.

Factorise :

27m3 – 216n3


Answer:

We know that


on comparison with above, we get


a = 3m, b = 6n



Note: Must memorize cubes upto 12



Question 4.

Factorise :

125y3 – 1


Answer:

We know that


on comparison with above, we get


a = 5y, b = 1



Note: Must memorize cubes upto 12



Question 5.

Factorise :

8p3 – 27/p3


Answer:

We know that


on comparison with above, we get


a = 2p, b = 3/p



Note: Must memorize cubes upto 12



Question 6.

Factorise :

343a3 – 512b3


Answer:

We know that


on comparison with above, we get


a = 7a, b = 8b



Note: Must memorize cubes upto 12



Question 7.

Factorise :

64x2 – 729y2


Answer:

We know that


on comparison with above, we get


a = 4x, b = 9y



Note: Must memorize cubes upto 12



Question 8.

Factorise :

16 a3 – 128/b3


Answer:

We know that


taking 2 common from above given equation;



on comparison with above, we get


a = 2a, b = 4/b




Note: Must memorize cubes upto 12



Question 9.

Simplify :

(x + y)3 – (x – y)3


Answer:

We know that


On comparing with given equation we get,


a = (3a + 5b), b = (3a – 5b)



Applying and






Question 10.

Simplify :

(3a + 5b)3 – (3a – 5b)3


Answer:

We know that


On comparing with given equation we get,


a = (3a + 5b), b = (3a – 5b)



Applying and






Question 11.

Simplify :

(a + b)3 – a3 – b3


Answer:

We know that


On comparing with given equation we get





Question 12.

Simplify :

p3 – (p + 1)3


Answer:

We know that


On comparing with given equation we get


a = p, b = 1





Question 13.

Simplify :

(3xy – 2ab)3 – (3xy + 2ab)3


Answer:

We know that


On comparing with given equation we get,


a = (3xy – 2ab), b = (3xy + 2ab)




Applying and








Practice Set 6.4
Question 1.

Simplify:



Answer:

We know that



applying these equation in above expression, we get



= 1


Note: - Try to factorize that term which help in reducing expression.



Question 2.

Simplify:



Answer:

We know that

and factorization of numerator and denominator





= a + 1


Note: - Try to factorize that term which help in reducing expression.



Question 3.

Simplify:



Answer:

We know that

and




Note: - Try to factorize that term which help in reducing expression.



Question 4.

Simplify:



Answer:

Applying and factorization, we get



= 1


Note: - Try to factorize that term which help in reducing expression.



Question 5.

Simplify:



Answer:

Applying

and factorization, we get, also changing by reversing N and D






Note: - Try to factorize that term which help in reducing expression.



Question 6.

Simplify:



Answer:

Applying

and factorization, we get





= x – 2


Note: - Try to factorize that term which help in reducing expression.



Question 7.

Simplify:



Answer:

Applying

, factorization and we get, also changing by reversing N and D





= 5a + 1


Note: - Try to factorize that term which help in reducing expression.



Question 8.

Simplify:



Answer:

Applying

and factorization, we get




Note: - Try to factorize that term which help in reducing expression.