# How do you multiply (3x - 5) ( 3x + 5)?

Mar 10, 2017

$9 {x}^{2} - 25$

#### Explanation:

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

substitute $a$ with $3 x$ and $b$ with $5$:

$\left(3 x + 5\right) \left(3 x - 5\right) = {\left(3 x\right)}^{2} - {5}^{2}$

$= 9 {x}^{2} - 25$

$\therefore \left(3 x + 5\right) \left(3 x - 5\right) = 9 {x}^{2} - 25$