Question

sin x+ sin4x+sin7x=0

Answer 1

Ответ:

$sin x+sin 4x+sin 7x=0$

$sin4x+2sin ((x+7x)/2)cos ((x+7x) /2)=0$

$sin4x+2sin 4x cos4x=0$

$2sin4xcos4x= -sin4x$

$cos4x=-1/2$

$4x=4\pi /3$

$x=\pi/3$