Question

Diketahui 10 cos x = -5 untuk 0 < x < π. Nilai x yang memenuhi persamaan tsb adalah?
Tolong pakai cara yaaa:)))

Answer 1

10 cos x = - 5
cos x = -5/10 = - 1/2 = - cos 60 = cos 120
cos x = cos 120 = cos 2π/3
x = 2π/3 + k. 2π  atau x = - 2π/3 +k. 2π
k = 0,1,2,3,....

k = 0 -->  x = 2π/3  atau x = - 2π/3  (tidak memenuhi)
k = 1 ---> x = 8π/3 (TM)  atau x = 4π/3

x = ( 2π/3 , 4π/3)