Sin8x\sin4x - 2cos(в степени 2 ) 2x = 2*sin4x*cos4x\sin4x - 2* (1+cos4x)\2= 2cos4x -1 - cos4x = cos4x - 1
Sin8x\sin4x - 2cos(в степени 2 ) 2x = 2*sin4x*cos4x\sin4x - 2* (1+cos4x)\2= 2cos4x -1 - cos4x = cos4x - 1