Cos5x+cos2x+cos3x+cos4x=0

(Cos 5x + Cos 2x) + (Cos3x + Cos 4x) = 0

2Cos3,5xCos1,5x + 2Cos3,5xCos0,5x=0

2 Cos3,5x (Cos1,5x+Cos0,5x) = 0

2Cos 3,5x·2CosxCos0,5x = 0

Cos 3,5x = 0 или Cos x = 0 или Cos0,5x = 0

3,5 х = π/2 + πк, к ∈Z; х = π/2 + πn, n ∈Z; 0,5x = π/2 + πm, m∈Z

х = π/7 + 7πк/2, к∈Z x = π + 2πm, m∈Z