cos^6x = cos^4x subtract cos^4x ffrom both sides
cos^6x - cos^4x = 0 faactor this
cos^4x*(cos^2x - 1) = 0
cos^4x (cosx + 1)(cosx-1) setting each factor to 0, we have
x = 0, pi/2, pi , (3 pi)/2 in the interval [0, 2pi)
More general solutions are x = 0 + (pi)n and x = pi/2 + (pi/2)n where n is an integer
