# pre-calc

posted by
**Jess** on
.

Solve:

cos(2x-180) - sin(x-90)=0

my work:

cos2xcos180 + sin2xsin180= sinxcos90 - sin90cosx

-cos2x - sin2x= cosx

-cos^2x + sin^2x -2sinxcosx=cosx

I'm stuck here. I tried subtracting cosx from both sides and making sin^2x into 1- cos^2x, but I still can't seem to solve the problem.