persamaan trigonometri

sin² 2x + 2 cos x = 0

sin² 2x = -2 cos x

(2 sin x cos x)² = -2 cos x

2 sin x cos x . sin x = -1

2 sin² x cos x = -1

2 cos x (1 – cos² x ) = -1

2 cos x – 2 cos³ x = -1

2 cos³ x – 2 cos x – 1 = 0

misal :

cos x = a

2a³ – 2a – 1 = 0

utk a ∈ R → a = 1,1915 (kalkulator)

cos x = 1,1915

tidak ada x bilangan real yg memenuhi

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