# How do you use the product to sum formulas to write #cos2thetacos4theta# as a sum or difference?

##### 1 Answer

Feb 17, 2017

#### Explanation:

Use trig identity:

In this case, we have:

Solving the system of equation (1) and (2), we get:

2a = 4 + 8 = 12 -->

There for: