jika tan a=12/5 dengan 180

Bab Trigonometri
Matematika SMA kelas X


tan a = 12/5.

1+tan^2 a = sec^2 a
1+ (12/5)^2 = sec^2 a
1 + 144/25 = sec^2 a
sec^2 a = 169/25
sec a = V169/V25
sec a = - 13/5.

sec a = 1 / cos a
Cos a= 1/ -13/5
Cos a= 1 x -5/13
Cos a= -5/13