# How do you find the exact value of cos(-30)?

Mar 17, 2018

color(brown)(cos (-30) = cos 30 = cos (pi/6) = sqrt3 / 2 = 0.866

#### Explanation:

To get exact value of $\cos \left(- 30\right)$

$\cos \left(- 30\right)$ is in IV quadrant where only cos and sec are positive.

Hence $\cos \left(- 30\right) = \cos 30 = \cos \left(\frac{\pi}{6}\right)$

From the above table,

color(brown)(cos (-30) = cos 30 = cos (pi/6) = sqrt3 / 2 = 0.866