# How do you simplify (6 + sqrt 5) (6 - sqrt5)?

Oct 15, 2015

$\left(6 + \sqrt{5}\right) \left(6 - \sqrt{5}\right) = 31$

#### Explanation:

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

Replacing $a$ with $6$
and $b$ with $\sqrt{5}$

$\left(6 + \sqrt{5}\right) \left(6 - \sqrt{5}\right)$

$\textcolor{w h i t e}{\text{XXX}} = \left({6}^{2} - {\left(\sqrt{5}\right)}^{2}\right)$

$\textcolor{w h i t e}{\text{XXX}} = \left(36 - 5\right)$

$\textcolor{w h i t e}{\text{XXX}} = 31$