Tolong matematika ini dong..

a. cotan 150° = cot (180°-30°)
                    = - cot 30°
                    =-√3
b. sec 135° = sec (180°- 45°)
                  = - sec 45°
                  = -√2 

c. sin 300° = sin (180°+120°)
                = -sin 120°
                = -1/2√3