Cos 4x+ cos 2x = 0 untuk 0《 x 《 2r

cos 4x + cos 2x = 0
2cos² 2x - 1 + cos 2x = 0
(2 cos 2x - 1)(cos 2x + 1) = 0
cos 2x = 1/2 atau cos 2x = -1

0 ≤ x ≤ 2π

cos 2x = 1/2
2x = 60° ---> x = 30° = π/6
2x = 300° ---> x = 150° = 5π/6
2x = 420° ---> x = 210° = 7π/6
2x = 660° ---> x = 330° = 11π/6

cos 2x = -1
2x = 180° --> x = 90° = π/2
2x = 540° --> x = 270° = 3π/2