Question

доказать тождество
2sin3a×cos4a+sina=sin7a

Answer 1

$2sin(3a)*cos(4a)+sin(a)=sin(7a)$
$2(\frac{sin(3a-4a)+sin(3a+4a)}{2})+sin(a)=sin(7a)$
$sin(-a)+sin(7a)+sin(a)=sin(7a)$
$-sin(a)+sin(7a)+sin(a)=sin(7a)$
$sin(7a)=sin(7a)$

тождество верно