Доказать тождество: (tg^2 a - sin^2 a) * ctg^2 a = sin^2 a.

Question

Доказать тождество:
(tg^2 a - sin^2 a) * ctg^2 a = sin^2 a.

Answer 1

(tg^2 a-sin^2 a)*ctg^2 a=sin^2 a
(tga*ctga)^2-sin^2 a*cos^2a/sin^2a
=1-cos^2 a=sin^2 a

sin^2 a=sin^2 a