Question

Доказать тождество 4sin^2a-4sin^4a=sin^2 2a

Answer 1

$4sin^2(a)-4sin^4(a)=sin^2(2a)\\4sin^2(a)(1-sin^2(a)=(2sin(a)cos(a))^2\\4sin^2(a)cos^2(a)=4sin^2(a)cos^2(a)$