Помогите sin(x+30)*sin(x-30)=1/4-sin^2x
Ответ
3
1/2(cos(x+30-x+30)-cos(x+30+x-30)=1/4-sin^2x
1/4-1/2cos2x-1/4+sin^2x=0
sin^2x-1/2cos2x=0
(1-cos2x)/2-1/2cos2x=0
1/2-cos2x=0
cos2x=1/2
2x=60градусов
х=30градусов