sin5x+sin7x+sin9x=0
sin7x+(sin5x+sin9x)=0
sin7x+2sin7xcos2x=0
sin7x*(1+2cos2x)=0
sin7x=0; 7х= πn; n∈Z; x= πn/7; n∈Z;
1+2cos2x=0
cos2x=-0.5
2х=±arccos(-0/5)+2πn; n∈Z
2х=±2π/3+2πn; n∈Z
х=±π/3+πn; n∈Z
sin5x+sin7x+sin9x=0
sin7x+(sin5x+sin9x)=0
sin7x+2sin7xcos2x=0
sin7x*(1+2cos2x)=0
sin7x=0; 7х= πn; n∈Z; x= πn/7; n∈Z;
1+2cos2x=0
cos2x=-0.5
2х=±arccos(-0/5)+2πn; n∈Z
2х=±2π/3+2πn; n∈Z
х=±π/3+πn; n∈Z