=cos^(2)x-sin^(2)x-((2tgx)/(1-tg^(2)x))*(1-tg^(2)x)+sin^(2)x-2tgx=
=cos^(2)x-2tgx-2tgx=cos^(2)x-4tgx.
[m]cos2x-tg2x(1-tg^2x)+sin^2x-2tgx=\underbrace{cos^2x-sin^2x}_{cos2x}-\underbrace{\frac{2tgx}{1-tg^2x}}_{tg2x}\cdot (1-tg^2x)+sin^2x-2tgx=cos^2x-4tgx[/m]