Sin3x+sin4x+sin5x=0
(sin3x+sin5x)+sin4x=0
2sin((3x+5x)/2)*cos((3x-5x)/2)+sin4x=0
2sin4x*cosx+sin4x=0
sin4x*(2cosx+1)=0
sin4x=0 или 2cosx+1=0
1. sin4x=0, 4x=πn, n∈Z |:4
x₁=πn/4, n∈Z
2. 2cosx+1=0, cosx=-1/2. x=+-arccos(-1/2)+2πn, n∈Z. x=+-(π-arccos(1/2))+2πn, n∈Z
x₂=+-(2π/3)+2πn, n∈Z