Cos(2x)+cos(4x)+cos(6x)=0

assume 0° ≤ x ≤ 360°cos 2x + cos 4x + cos 6x = 0cos 4x + (cos 2x + cos 6x) = 0cos 4x + (2 cos 4x cos 2x) = 0(1 + 2 cos 2x) cos 4x = 0(1 + 2 cos 2x) = 0cos 2x = -½2x = 120°x = 60°or2x = 240°x = 120°orcos 4x = 04x = 90°x = 22.5°or4x = 270°x = 67.5°x = 22.5° , 60° , 67.5° , 120°