# Half angle identities?

## tan pi/12=tan (pi/6)/2

Jul 24, 2018

As below.

#### Explanation:

Special cases of the sum and difference formulas for sine and cosine yields what is known as the double‐angle identities and the half‐angle identities.

In addition to the above, sine and cosine can be expressed in terms of tangent also.

$\sin 2 \theta = \frac{2 \tan \theta}{1 + \tan 62 \theta}$

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