Question

Question #0299e

Answer 1

The answer is `=cos(3x)`

Explanation:

Apply the following

`cos(a-b)=coacosb+sinasinb`

Here,

`a=5x` and `b=2x`

Therefore,

`cos(5x)cos(2x)+sin(5x)sin(2x)=cos(5x-2x)=cos(3x)`