1. The problem statement, all variables and given/known data How can I write cos(x) in terms of cot(x)? I tried using the pythagorean identities and fundamental identities but still cannot figure it out. The answer must start as the following: cosine(x)=..... 2. Relevant equations All the trig identies. I think it wants me to use the fundamental ones but Im not sure thats possible http://www.sosmath.com/trig/Trig5/trig5/trig5.html 3. The attempt at a solution I know that cotangent=cos/sin but I need it to only be in terms of cosine which seems impossible to me because I've tried everything. Also, I do believe it is okay to use cot^2(x) with the pythagorean identities.