Question

$36a^2-81canbefactorizedas$______.

• A. $(6a+81)(6a-81)$
• B. $(6a-9)(36a+9)$
• C. $(6a+9)(6a-9)$
• D. $(36a+9)(36a-9)$

Answer 1

The correct option is C $(6a+9)(6a-9)$

$36a^2-81$ is in the form of $x^2-y^2.$
So, the identity $x^2-y^2=(x+y)(x-y)$
can be used.
$\Rightarrow 36a^2-81=(6a{)}^2-9^2=(6a+9\left)\right(6a-9)$