Выражение: tg^2 x-sin^2 x-tg^2 x*sin^2 x=

(sin^2 x)/(cos^2 x) - ((sin^2 x)*(cos^2 x)/(cos^2 x)) - (sin^4 x)/(cos^2 x) = (sin^2 x)*(1- cos^2 x) - (sin^4 x)/(cos^2 x) = (sin^2 x)*(sin^2 x)/(cos^2 x) - (sin^4 x)/(cos^2 x) = 0