Summing cosines of sines and cosines

[matlabber]

Homework Statement

$$\sum_{t=0}^{n-1}cos2 \pi ft(x_{t}- \mu-Acos2 \pi ft-Bsin2 \pi ft)$$

Homework Equations

The Attempt at a Solution

I know to set = 0
I just am not knowing what to do with the cos after the sum...how do I take this sum?

 

[tiny-tim]

hi matlabber!

i suspect they mean $\sum_{t=0}^{n-1}(cos2 \pi ft)(x_{t}- \mu-Acos2 \pi ft-Bsin2 \pi ft)$