Question

Соs3x= -sinx*sin2x решите уравнение

Answer 1

$cos3x= -sinx*sin2x;$
$cos(x+2x)= -sinx*sin2x;$
$cosxcos2x-sinx*sin2x= -sinx*sin2x;$
$cosxcos2x=0;$
$cosx=0;x= frac{ pi }{2}+ pi n, n in Z;$
$cos2x=0;2x=frac{ pi }{2}+ pi n, n in Z;x=frac{ pi }{4}+ frac{ pi }{2} n, n in Z;$