Question

Cos2a (1+ tg^2a)-1
УПРОСТИТЬ

Answer 1

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