# How do you evaluate cos315?

Jul 30, 2016

This is how we do it:

#### Explanation:

$\cos \left(315\right)$
$= \cos \left(360 - 45\right)$

$= \cos 45$
(as cos is positive in 4th quadrant and its function also remains same)

$= \frac{1}{\sqrt{2}}$