sin10xsin2x =sin8xsin4x

Решим уравнение.

sin (10 * x) * sin (2 * x) = sin (8 * x) * sin (4 * x); 

1/2 * (cos (10 * x - 2 * x) - cos (10 * x + 2 * x)) = 1/2 * (cos (8 * x - 4 * x) - cos (8 * x+  4 * x)); 

(cos (10 * x - 2 * x) - cos (10 * x + 2 * x)) =  (cos (8 * x - 4 * x) - cos (8 * x+  4 * x)); 

cos (8 * x) - cos (2 * x) =  (cos (4 * x) - cos (12 * x);  

cos (8 * x) = cos (4 * x); 

cos (8 *x) - cos (4 * x) = 0; 

-2 * sin ((8 * x + 4 * x)/2) * sin ((8 * x -   4 * x)/2) = 0;  

sin (6 * x) * sin (2 * x) = 0; 

1) sin (6 * x) = 0; 

x = pi/6 * n; 

2) sin (2 * x) = 0; 

x = pi/2 * n.