Tentukan nilai cos (270°+30°) …. tolong

CARA 1 :
cos (270 + 30) = cos 300 = cos (360 – 60) = cos 60 = 1/2

CARA 2 :
cos 270 = 0
sin 270 = -1

cos (270 + 30) = cos 270. cos 30 – sin 270. sin 30

= (0. cos 30) – (-1. sin 30)

= 0 + sin 30

= 1/2

Misal a=270° , b=30°
Cos (a+b)=cosa.cosb-sina.sinb
cos (a+b)=0.√3/2-(-1)(1/2)
Cos (a+b)=1/2