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# Find the Values of P and Q So that X4 + Px3 + 2x3 − 3x + Q is Divisible by (X2 − 1). - CBSE Class 9 - Mathematics

ConceptFactorisation of Polynomials

#### Question

Find the values of p and q so that x4 + px3 + 2x3 − 3x + q is divisible by (x2 − 1).

#### Solution

Let  f(x) =  x4 + px3 + 2x3 − 3x + q and g(x) = x^2 - 1be the given polynomials.

We have,

g(x)= x^2 - 1

 = (x-1)(x+ 1)

Here,  (x-1),(x+1)are the factor of g(x).

If f(x) is divisible by (x-1)and (x+1), then (x-1)and (x+1) are factor of f(x).

Therefore, f(1) and f(−1) both must be equal to zero.

Therefore,

f(1) = (1)^4 + p(a)^3 + 2(1)^2 - 3(1)+q    ......... (1)

⇒ 1+ p + 2 - 3 + q = 0

p+q = 0

and

f(-1) = (-1)^4 + p(-1)^3 + 2(- 1)^2 - 3(-1) + q = 0

 1-p+2 + 3 +q = 0

-p + q = -6         ......(2)

Adding both the equations, we get,

(p+q) + (-p + q) = -6

2q = -6

q = -3

Putting this value in (i)

p+(-3) = 0

p = 3

Hence, the value of p and q are 3, −3 respectively.

Is there an error in this question or solution?

#### APPEARS IN

RD Sharma Solution for Mathematics for Class 9 by R D Sharma (2018-19 Session) (2018 to Current)
Chapter 6: Factorisation of Polynomials
Ex.6.40 | Q: 19 | Page no. 25

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Solution Find the Values of P and Q So that X4 + Px3 + 2x3 − 3x + Q is Divisible by (X2 − 1). Concept: Factorisation of Polynomials.
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