Question

Научите доказывать тождества пж.

Answer 1

например вот так
$tg^2 alpha - sin^2 alpha = frac{sin^2 alpha }{cos^2 alpha } - sin^2 alpha = frac{sin^2 alpha - sin^2 alpha * cos^2 alpha }{cos^2 alpha } = frac{sin^2 alpha *(1-cos^2 alpha )}{cos^2 alpha }$

$\ frac{sin^2 alpha *sin^2 alpha }{cos^2 alpha } = sin^2 alpha *tg^2 alpha$