So I need a method to find the intercepts for two trig equations: y = sinx - cosx and y = 2cos(2x). I know that substitution is supposedly the easiest, but I can't seem to get anything usable. The segment I'm using is below. The actual intercepts are -1.1468, 1.3229 for the left and 0.7854, 0 for the right, but I need an algebraic/trigonometric/whatever way to do it.

Cheers.