# Question #bf293

Aug 28, 2016

not a valid identity.

#### Explanation:

Here the left side ≠ right side as the left side equals zero, since they are 'like terms"

$\Rightarrow \cos \left(x + y\right) - \cos \left(x + y\right) = 0$

Aug 28, 2016

The left side is 0.

#### Explanation:

Let's say cos(x=y) represents x. When we plug x in, x-x definitely =0.