# How do you use the difference of two squares formula to factor 4x^2 − 81?

May 9, 2015

The geeral form for the difference of squares is
#a^2-b^2)=(a+b)(a-b)

For the given example
$4 {x}^{2} - 81$

$= {\left(2 x\right)}^{2} - {9}^{2}$

$= \left(2 x + 9\right) \left(2 x - 9\right)$