# Math Help - "Prove that" question

1. ## "Prove that" question

If cos(a-b) + cos(b-c) + cos(c-a) = 3/2,
the prove that cos(a) + cos(b) + cos(c) = sin(a) + sin(b) + sin(c) = 0.

2. ## Re: "Prove that" question

did you even try?

expand out the first line using $\cos(x-y)=\cos(x)\cos(y)+\sin(x)\sin(y)$ and see where that leads.