mohon bantuannya yah !

Trigonometri

No.5
cos 4x - cos 2x = 0, interval 0 ≤ x ≤ 2π
2cos²2x - 1 - cos 2x = 0
2cos²2x - cos 2x - 1 = 0
(2cos 2x + 1)(cos 2x - 1) = 0
Untuk 
cos 2x = - ¹/₂
2x = (π - π/3), atau (π + π/3)
2x = ²/₃.π ⇒ x = π/3
2x = ⁴/₃.π ⇒ x = 2π/3
Untuk
cos 2x = 1
2x = 0, atau 2π
2x = 0 ⇒ x = 0
2x = 2π ⇒ x = π

Jadi HP = {x | 0, π/3, 2π/3, π}

No.6
sin (x + π/4) = cos x
sin x. cos π/4 + cos x. sin π/4 = cos x
¹/₂.√2.sin x + ¹/₂.√2.cos x = cos x
¹/₂.√2.sin x = (1 - ¹/₂.√2)cos x

(sin x) / (cos x) = [1 - ¹/₂.√2] / [¹/₂.√2]

tan x = [tex] \frac{1- \frac{1}{2} \sqrt{2} }{ \frac{1}{2} \sqrt{2} } [/tex]

tan x = [tex]\frac{2- \sqrt{2} }{ \sqrt{2} } [/tex]

tan x = [tex]\frac{2\sqrt{2}-2 }{2}= \sqrt{2}-1 [/tex]