Question

Доказать тождество $frac{cos^{2}a-sin^{2}a }{sina cosa} = frac{1-tg^{2}a }{tga}$

Answer 1

$frac{1-tg^2alpha }{tgalpha } =frac{1-frac{sin^2alpha }{cos^2alpha } }{frac{sinalpha }{cosalpha } } =frac{frac{cos^2alpha-sin^2alpha }{cos^2alpha } }{frac{sinalpha }{cosalpha } } =frac{cos^2alpha -sin^2alpha }{sinalphacdot cosalpha }$