# How do you factor 4x^2 - 81?

Nov 14, 2015

color(blue)((2x+9)(2x-9)

#### Explanation:

4x^2−81 can also be expressed as
${\left(2 x\right)}^{2} - {9}^{2}$

Now as per the property :
color(blue)(a^2-b^2=(a+b)(a-b) we can re write the expression.

color(blue)((2x)^2-9^2= (2x+9)(2x-9)
(here a=2x, b=9)

So the factorised form for the expression is
color(blue)((2x+9)(2x-9)