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.