Jawabanmu

2014-03-21T17:40:39+07:00
cos 2x – 5 cos x – 2 = 0 
cos²x – 1 – 5 cos x – 2 = 0 
2cos²x – 5 cos x – 3 = 0 
(2 cos x + 1) (cos x – 3) = 0 
cos x = -½ atau cos x = 3 (TM) 

cos x = -½ 
cos x = cos 120⁰ (TM) atau cos x = cos 240⁰ 

cos x = cos 240⁰ 
x = 240⁰ 

tan x = tan 240⁰ = √3