Question

1-cos^2x+tg^2xcos^2x-2sin^2x

Answer 1

1 - cos^2x + tg^2x * cos^2x - 2sin^2x = 1 - cos^2x + (sin^2x*/cos^2x)*cos^2x - 2sin^2x = cos^2x + sin^2x + sin^2x - 2sin^2x = 0