Cos9*x-cos5*x=3sin2*x

Cos(9x) - cos(5x) = 3sin(2x);
-2sin((9x + 5x)/2)sin((9x - 5x)/2) + 3sin(2x) = 0;
-2sin(7x)sin(2x) + 3sin(2x )= 0;
sin(2x)(3 - 2sin(7x))= 0;
1. sin(2x) = 0;
2x = пn;
x = пn/2;
2. (3 - 2sin(7x))= 0;
sin(7x) = 3/2;
7x = п/3 + 2пn;
7x = 2п/3 + 2пn;
x = (-1)^n (п/21) + пn/7;