cos2x + cos^2(pi/2 + x) = cos^2x - sin^2x + cos^2(pi/2) - sin^2(pi/2) = cos^2x - sin^2x + 0 - 1 = cos^2x - sin^2x - 1
cos2x + cos^2(pi/2 + x) = cos^2x - sin^2x + cos^2(pi/2) - sin^2(pi/2) = cos^2x - sin^2x + 0 - 1 = cos^2x - sin^2x - 1