Докажите тождества: А) sin^4a-cos^4a=sin^2a-cos^2a Б) sin a/1-cos a = 1+cos a/sin a

Question

Докажите тождества: А) sin^4a-cos^4a=sin^2a-cos^2a Б) sin a/1-cos a = 1+cos a/sin a

Answer 1

А) (sin^2a)^2)-(cos^2a)^2)=(sin^2a-cos^2a)(sin^2+cos^2a)=(sin^2a-cos^2)*1=sin^2-cos^2