# How do you factor 81x ^ { 2} - 144?

Jan 27, 2017

The answer is $= 9 \left(3 x + 4\right) \left(3 x - 4\right)$

#### Explanation:

We use

${a}^{2} - {b}^{2} = \left(a + b\right) \left(a - b\right)$

Therefore,

$81 {x}^{2} - 144 = 9 \left(9 {x}^{2} - 16\right)$

$= 9 \left(3 x + 4\right) \left(3 x - 4\right)$