My past instructor said that in a formal proof always start from one side to get to the other and not to alter the other side.
I'm sure if you can solve it by adding a one on the other side of the equation you can also solve it without.
sin^2(x)-sin^2(2x)=cos^2(2x)-cos^2(x)
I need help with proving this trig identity. Every thing I've tried just makes the problem more confusing. How would you guys go about this?