Вот.
cos(x)*cos(2x)*cos(4x)*cos(8x)=1/16
Пусть sin(x)≠0
2*sin(x)*cos(x)*cos(2x)*cos(4x)*cos(8x)/2=sin(x)/16
sin(2x)*cos(2x)*cos(4x)*cos(8x)/2=sin(x)/16
(sin(0)+sin(4x))*cos(2x)*cos(4x)*cos(8x)/4=sin(x)/16
sin(4x)*cos(4x)*cos(8x)/4=sin(x)/16
sin(8x)*cos(8x)/8=sin(x)/16
sin(16x)/16=sin(x)/16
sin(16x)-sin(x)=0
2*sin(7,5x)*cos(8,5x)=0
sin(7,5x)=0 x1=2пк/15 kЄZ k≠0
cos(8,5x)=0 x2=п/17+2пm/17 mЄZ