Решить уравнение! cos 5x×cos3x×cosx=-sin5x×sin3x×cosx

Cos5x•cos3x•cosx = -sin5x•sin3x•cosx
cos5x•cos3x•cosx + cosx•sin5x•sin3x = 0
cosx(cos5x•cos3x + sin5x•sin3x) = 0
cosx(cosx(5x - 3x)) = 0
cosx•cos2x = 0
cosx = 0
x = π/2 + πn, n ∈ Z
cos2x = 0
2x = π/2 + πn, n ∈ Z
x = π/4 + πn/2, n ∈ Z.