Sin15x*sin3x+cos7x*cos11x=0

sin15x · sin3x + cos7x · cos11x = 0;1/2(cos(15x - 3x) - cos(15x + 3x)) + 1/2(cos(7x - 11x) + cos(7x + 11x)) = 0;1/2 cos12x - 1/2 cos18x + 1/2 cos4x + 1/2 cos18x = 0;1/2(cos12x + cos4x) = 0;cos((12x + 4x) / 2) · cos((12x - 4x) / 2) = 0;cos8x = 0; 8x = π/2 + πn; x = π/16 + πn/8; n∈Z; илиcos4x = 0;4x = π/2 + πk;x = π/8 + πk/4; k∈Z;