## Answers

It's true for **all values of #x#**. We are to

**prove it as an identity**.

#### Explanation:

You can prove it using the formula for the sine and cosine of a sum.

Recall that

**sine of a sum**).

**cosine of a sum**).

First put in

**double angle identity for sine**).

**double angle identity for cosine**).

Now, repeat but this time set

**triple angle identity for sine**).

And the identity ee originally set out to prove:

**triple angle identity for cosine**).