Apabila tan x = 6/5, maka nilai cos 2x adalah ...

Trigonometri

tan x = 6/5
Berarti
a = 6
b = 5
c = √(6² + 5²)
c = √(36 + 25)
c = √61
cos x = 5/√61

cos 2x = 2 cos²x - 1
cos 2x = 2 (5/√61)² - 1
cos 2x = 2 (25/61) - 1
cos 2x = 50/61 - 1
cos 2x = 50/61 - 61/61
cos 2x = -11/61