Cos x/4*sin π/5-sin x/4*cos π/5=-√2/2

Cos x/4*sin π/5-sin x/4*cosπ5=-√2/2Cos x/4*sin π/5-sin x/4*cosπ/5 = - (√2) / 2;

Cos (x/4 + π/5) = - (√2) / 2;

x/4 + π/5 = +,-3π/4 + 2π*n;

x + 4π/5 = +,-3π + 8π*n, n∈Z.

x = (+,-) 3π - 4π/5 + 8π*n, n∈Z.

x₁ = 11π/5 + 8π*n, n∈Z;

x₂ = - 19π/5 + 8π*n, n∈Z.

ответ: 11π/5 + 8π*n,-19π/5 + 8π*n, n∈Z.