Question

$x^2+18x+77$ = .

• A. $(x-7)(x-11)$
• B. $(x-7)(x+11)$
• C. $(x+7)(x-11)$
• D. $(x+7)(x+11)$

Answer 1

The correct option is D $(x+7)(x+11)$

Given: $x^2+18x+77$.
Comparing the given expression with the identity $x^2+(a+b)x+ab$ we have,
$ab=77and(a+b)=18.$
$So,11+7=18and\left(11\right)\left(7\right)=77$.

Hence,
$x^2+18x+77$
= $x^2+11x+7x+77$
= $x(x+11)+7(x+11)$
= $(x+7)(x+11)$