Question

Solve into factors :
$a^2-9b^2$

Answer 1

$\begin{array}{c}{a}^2-9b^2=a^2-{\left(3b\right)}^2\\ Applytheformula,\\ \left(a^2-b^2\right)=\left(a+b\right)\left(a-b\right)\\ a^2-{\left(3b\right)}^2=\left(a-3b\right)\left(a+3b\right)\end{array}$

Hence, the factor is $\left(a-3b\right)\left(a+3b\right)$