nilai dari : cos 20° cos 40° cos 60° cos 80°

Halo Tresyah, kaka bantu jawab ya. Jawaban : 1/16 Konsep : Trigonometri Ingat bahwa : sin 2x = 2sin x cos x cos x = sin 2x / 2 sin x Dengan demikian; cos 20° cos 40° cos 60° cos 80° = (sin40°/2sin20°)(sin80°/2sin40°)(sin120°/2sin60°)(sin160°/2sin80°) =(1/2sin20°)(1/2)(sin120°/2sin60°)(sin160°/2) =(sin120° sin160°)/(16 sin20° sin60°) Sudut berelasi pada kuadran II sin(180°-x)=sin x maka, sin 120° = sin(180°-60°) sin 120° = sin60° sin 160° = sin(180°-20°) sin 160° = sin20° cos 20° cos 40° cos 60° cos 80° =(sin120° sin160°)/(16 sin20° sin60°) cos 20° cos 40° cos 60° cos 80° =(sin60° sin20°)/(16 sin20° sin60°) cos 20° cos 40° cos 60° cos 80° =1/16 Jadi, cos 20° cos 40° cos 60° cos 80° =(sin60° sin20°)/(16 sin20° sin60°)