Question

Докажите тождества sin^4a-cos^4a=sin^2a-cos^2a

Answer 1

sin^4a-cos^4a=sin^2a-cos^2a
(sin^2a-cos^2a)(sin^2a+cos^2a)=sin^2a-cos^2a
(sin^2a-cos^2a)*1=sin^2a-cos^2a
sin^2a-cos^2a=sin^2a-cos^2a