Factories: x^2-4 x-21 - Vidyadip

Question

Factories:
$x^2-4 x-21$

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Answer

To factories $x^2-4 x-21$, we will find two number $p$ and $q$ such that $p+q=-4$ and $p q=-21$
Now,
$3+(-7)=-4 \text { And } 3 \times(-7)=-21$
Splittiong the middle term $14 a$ in the given quadratic as $-7 x+3 x$, we get:
$x^2-4 x-21=x^2-7 x+3 x-21$
$=(x 2-7 x)+(3 x-21)$
$=x(x-7)+3(x-7)$
$=(x-7)(x+3)$

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