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All questions of Factorisation for Class 8 Exam

Factorise: x2+ 8x + 16
  • a)
    (x+ 3)2
  • b)
    (x+ 2)2
  • c)
    (x+ 4)2
  • d)
    (x+ 5)2
Correct answer is option 'C'. Can you explain this answer?

Geetika Shah answered
C ) (x2 +8x +16)
= (x2 + 4x + 4x + 16)
= ( x2 + 4x ) + (4x + 16 )
= x(x + 4 ) +4(x + 4 )
=(x + 4)(x + 4)
=(x + 4)2 

What are the factors of ax+by+bx+az+ay+bz?
  • a)
    (bx+ay),(ax+by)
  • b)
    (a+b),(2x+2y+2z)
  • c)
    (x+y+z),(a+b)
  • d)
    (x+y−z),(a−b)
Correct answer is option 'C'. Can you explain this answer?

Geetika Shah answered
ax+by+bx+az+ay+bz, rearranging we get ax+ay+az+bx+by+bz
a(x+y+z)+b(x+y+z)=(a+b)(x+y+z). Hence the factors are (a+b), (x+y+z)

Factorize x² + 8x + 12
  • a)
    (x + 2)(x + 6)
  • b)
    (x + 3)(x + 4)
  • c)
    3x + 12
  • d)
    3x - 12
Correct answer is option 'A'. Can you explain this answer?

Kaavya Saha answered
x² + 8x + 12 
two no whose product is 12 and sum is 8
ie. 2 and 6 so;
x2+2x+6x+12
x(x+2)+6(x+2)
(x+2)(x+6)

What are the factors of x4+2x2+9?
  • a)
    (x2+2x+3), (x2−2x+3)
  • b)
    (x2+3), (x2−3)
  • c)
    (x2+2x+3), (x2+2x+3)
  • d)
    (x2+3), (x2+3)
Correct answer is option 'A'. Can you explain this answer?

Given equation is x4 + 2x2 + 9
We can rewrite this as,
(x2)2 + 6x2 + 9 − 4x2
⇒ (x2 + 3)2 − (2x)2
....Since a2 + 2ab + b2 = (a+b)2
⇒ x4 + 2x2 + 9 = (x2 − 2x + 3)(x2 + 2x + 3)     
....Since a− b2 = (a+b)(a−b)

Which of the following is quotient obtained on dividing –18 xyz2 by –3 xz?
  • a)
    6 Yz
  • b)
    –6 yz
  • c)
    6 xy2
  • d)
    6 xy
Correct answer is option 'A'. Can you explain this answer?

Geetika Shah answered
–18 xyz2/–3 xz   x and x gets cancelled,-18 gets divided by -3 .and z2 gets divided by z so only one z remain in numerator So the quotient obtained is 6yz

What is the coefficient of 'a' when 9a2+18a is divided by (a+2)?
  • a)
    18
  • b)
    9
  • c)
    1/2
  • d)
    2
Correct answer is option 'B'. Can you explain this answer?

Coefficient of a when 9a^2 - 18a is divided by (a - 2)

To find the coefficient of a, we need to perform long division as shown below:

9a - 18
(a - 2) | 9a^2 + 0a - 18
9a^2 - 18a
------------
18a - 18
18a - 36
--------
18

Therefore, the remainder is 18 and the quotient is 9a + 18. The coefficient of a in the quotient is 9, so the answer is option B) 9.

How many factors does (x9−x) have?
  • a)
    9
  • b)
    4
  • c)
    2
  • d)
    5
Correct answer is option 'D'. Can you explain this answer?

Vivek Rana answered
f(x) = x9- x

The degree of f(x) = 9

So , this polynomial will have 9 zeros

therefore it will have 9 factors

Factorise: p4– 81
  • a)
    (p – 3) (p + 3) (p2+ 9)
  • b)
    (p + 3) (p2+ 9)
  • c)
    (p – 3) (p + 3)
  • d)
    none of these
Correct answer is option 'A'. Can you explain this answer?

Malavika Basu answered
We have  p4 - 81 = (p2)2 - (9)2 
 
Now using a2 - b2 = (a + b)(a - b), we have
 
         (p2)2 - (9)2 = (p2 + 9)(p2 -9)
 
We can factorise p2 - 9  further as
              p2 - 9 = (p)2 - (3)2
 
                       = (p + 3)(p - 3)
 
∴           p4 - 81 = (p + 3)(p - 3)(p2 + 9)

Can you explain the answer of this question below:

Factorise: 4y2−12y+ 9

  • A:

    (7y− 5)2

  • B:

    (5y− 3)2

  • C:

    (2y− 5)2

  • D:

    (2y− 3)2

The answer is D.

Kavya Saxena answered
We have 4y- 12y+9. comparing the equation with (a-b)2=a2-2ab+b2,gives us a2=(2y)2,2ab=2*3*2y and b2=(3)2.Hence the answer is (2y-3)2.

When we factorise an expression, we write it as a ________ of factors.
  • a)
    product
  • b)
    difference
  • c)
    sum
  • d)
    none of these
Correct answer is option 'A'. Can you explain this answer?

Aditya Shah answered
When we factorise an algebraic expression, we write it as a product of factors. These factors may be numbers, algebraic variables or algebraic expressions. 

Which of the following are the factors of 
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Riddhi Chhabra answered
X²/4 - y²/9
Taking both in brackets of square as 2² is 4 and 3² is 9
(x/2)²-(y/3)²
now using the property (a-b)²=(a+b)(a-b)
(x/2+y/3) (x/2-y-3)

Hence the answer is option C .

For x2+2x+5 to be a factor of x4+ px2+q, what must the respective values of p and q be?
  • a)
    −2 and 5
  • b)
    5 and 25
  • c)
    10 and 20
  • d)
    6 and 25
Correct answer is option 'D'. Can you explain this answer?

Neha Banerjee answered
x^4+px^2+q.

=x^2(x^2+2x+5)-2x^3–5x^2+px^2+q.

=x^2(x^2+2x+5)-2x(x^2+2x+5)+4x^2+10x-5x^2+px^2+q.

=x^2(x^2+2x+5)-2x(x^2+2x+5)+(p-1). x^2+10x+q.

=x^2(x^2+2x+5)-2x(x^2+2x+5)+(p-1)(x^2+2x+5)-2(p-1).x-5(p-1)+10x+q.

=(x^2+2x+5) (x^2–2x+p) +2(6-p).x+5(1-p)+q.

=Divisor � Q +R.

Remainder = 0

2(6-p).x+(5–5p+q)= 0.

2(6-p)x+(5–5p+q)= 0.x + 0.

Equating the coeff. of x and constant term.

2(6-p) = 0 => p = 6 and

5–5p+q = 0.

5–5�6+q = 0.

q = 30–5 = 25

p = 6 and q = 25 , Answer.

Divide the given polynomial by the given monominal: 8 (x3y2z2 + x2y3z2 + x2y2z3) ÷ 4x2y2z2
  • a)
    (x + y + z)
  • b)
    2(x + y + z)
  • c)
    2
  • d)
    none of these
Correct answer is option 'B'. Can you explain this answer?

Nitin Sen answered
To divide a polynomial by a monomial, we need to divide each term in the polynomial by the monomial.

Given polynomial: 8x^3y^2z^2 - x^2y^3z^2 - x^2y^2z^3
Given monomial: 8

Dividing each term by the monomial 8:

(8x^3y^2z^2)/8 = x^3y^2z^2
(-x^2y^3z^2)/8 = -1/8 * x^2y^3z^2
(-x^2y^2z^3)/8 = -1/8 * x^2y^2z^3

Therefore, the result of dividing the given polynomial by the monomial 8 is:

x^3y^2z^2 - (1/8)x^2y^3z^2 - (1/8)x^2y^2z^3

Which of the following is one of the factors of x4+4?
  • a)
    x2+2
  • b)
    (x² + 2 + 2x)(x² + 2 - 2x)
  • c)
    x2−2
  • d)
    x2+2x−2
Correct answer is option 'B'. Can you explain this answer?

Amrutha Saini answered
x4+4
adding and subtracting  4x2
x4+4+4x2−4x2
(x2)2+22+2∗2∗x2−(2x)2
(x2+2)2−(2x)2(a+b)2=a2+b2+2ab
(x2+2−2x)(x2+2+2x)(a2−b2)=(a+b)(a−b)

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