# How do you factor 81x^4 -256?

Apr 18, 2018

$\left(9 {x}^{2} + 16\right) \left(3 x + 4\right) \left(3 x - 4\right)$

#### Explanation:

Using the difference of two squares (${a}^{2} - {b}^{2} = \left(a + b\right) \left(a - b\right)$) we can get:
$\left(9 {x}^{2} + 16\right) \left(9 {x}^{2} - 16\right)$

$9 {x}^{2} - 16 = \left(3 x + 4\right) \left(3 x - 4\right)$

$\left(9 {x}^{2} + 16\right) \left(3 x + 4\right) \left(3 x - 4\right)$