Answer:
2cosx cosy = 2cosx cosy
Step-by-step explanation:
cos(x+y) + cos(x-y) = 2cosx cosy
Use the formula for "Functions of the sum of two angles" and the "Function of the Difference of Two Angles" and substitute that in.
(Cosx cosy - sinx siny) + (cosx cosy + sinx siny)
Drop the parentheses
Cosx cosy - sinx siny + cosx cosy + sinx siny
Sinx siny can cancel
Cosx cosy + cosx cosy
This can be simplified to
2cosx cosy
