# Factorize Each of the Following Algebraic Expression: X2 − 4x − 21 Answer 10: - Mathematics

Sum

Factorize each of the following algebraic expression:
x2 − 4x − 21

#### Solution

$\text{ To factorise }x^2 - 4x - 21,\text{ we will find two numbers p and q such that }p + q = - 4\text{ and }pq = - 21 .$
Now,
$3 + ( - 7) = - 4$
and
$3 \times ( - 7) = - 21$
$\text{ Splitting the middle term }- 4x\text{ in the given quadratic as }- 7x + 3x, \text{ we get: }$
$x^2 - 4x - 21 = x^2 - 7x + 3x - 21$
$= ( x^2 - 7x) + (3x - 21)$
$= x(x - 7) + 3(x - 7)$
$= (x + 3)(x - 7)$

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#### APPEARS IN

RD Sharma Class 8 Maths
Chapter 7 Factorization
Exercise 7.7 | Q 10 | Page 27