# Math Help - Simplifying trig problem

1. ## Simplifying trig problem

Hi guys, I need help on simplifying this trig equation, any help appreciated

I have to show that

cos((n+1).X) = 2cosn X .cosX - cos((n-1).X)

But I do not know what steps to take.

EDIT: I think this is in the wrong forum. sorry.

2. Use the identity $\cos a+\cos b=2\cos\frac{a+b}{2}\cos\frac{a-b}{2}$

for $\cos(n+1)x+\cos(n-1)x$