Question

Докажите
Tg2a-tga=tga/cos2a

Answer 1

Ответ:

tg a / (2tg a/(1-tg^2 a) — tg a) = (1-tg^2 a)/ (2-1+tg^2 a) =

= (1-tg^2 a)/ (1+tg^2 a) = (cos^2 a — sin ^2 a) * cos ^2 a/ cos ^2 a =

= cos 2a