Question

Докажите тождество :
4sina cosa × cos2a=sin4a

Answer 1

$4 sin(a) cos(a) times cos(2a) = sin(4a) \ \ 4 sin(a) cos(a) times cos(2a) = 2 times 2sin(a) cos(a) times cos(2a) = \ = 2 sin(2a) cos( 2a ) = sin(2 times 2a) = sin(4a) \ \ sin(4a) = sin(4a)$