Question

tg^2a*cos^2a-cos^2a/cos 2a помогите пож

Answer 1

$frac{tg^2 alpha cdot cos^2 alpha -cos^2 alpha }{cos2 alpha }=frac{frac{sin^2 alpha }{cos^2 alpha }cdot cos^2 alpha -cos^2 alpha }{cos2 alpha }=frac{sin^2 alpha -cos^2 alpha }{cos2 alpha }=\\=frac{-(cos^2 alpha -sin^2 alpha )}{cos2 alpha }=frac{-cos2 alpha }{cos2 alpha }=-1$