# How do you use double angle identities to solve equations?

Mar 9, 2018

As below.

#### Explanation:

Following table gives the double angle identities which can be used while solving the equations.

You can also have $\sin 2 \theta , \cos 2 \theta$ expressed in terms of $\tan \theta$ as under.

$\sin 2 \theta = \frac{2 \tan \theta}{1 + {\tan}^{2} \theta}$

$\cos 2 \theta = \frac{1 - {\tan}^{2} \theta}{1 + {\tan}^{2} \theta}$