diketahui cos 130 - cos 110 = p . nilai cos 20 =

Halo, selamat malam.

Kita pakai rumus :

cos x-cos y = -2 sin (x+y)/2 sin (x-y)/2

cos 130 - cos 110 = p

cos 130 - cos 110 = -2 sin 120 sin 10

sin 120 = 1/2 akar 3

p =  -2 . 1/2 akar 3 sin 10

p = - akar 3 sin 10

sin 10 = -1/3 akar 3 p

cos 20 = cos (2.10)

mis 10 = x

cos 2x = 1-2sin^2 x

cos 20 = 1 - 2(-1/3 akar 3 p)^2
cos 20 = 1 - 2 . 1/3 p^2
cos 20 = 1 - 2/3 p^2

semoga terbantu :) mohon maaf jika salah, malam :D