cos2x<=cos3x-cos4x

cos2x≤cos3x-cos4x

cos2x+cos4x≤cos3x

2cos3x cosx≤cos3x, 2cos3x cosx-cos3x≤0

cos3x (2cosx-1) ≤0

1) {cos3x≤0 2) {cos3x>0

{2cosx-1>0 {2cosx-1≤0

{ π/2+2πn≤ 3x ≤3π/2+2πn {-π/2+2πm<3x<π/2+2πm

{ cosx>1/2 { cosx≤1/2

{π/6+2πn/3≤x≤π/2+2πn/3 {-π/6+2πm/3
{-π/3+2πk
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