(1)cos(-420°) (2)cos(-2040°)

问题描述:

(1)cos(-420°) (2)cos(-2040°)

cos(-420°)
=cos(420)
=cos(360+60)
=cos60
=1/2
cos(-2040°)
=cos(-360*6+120)
=cos120
=-cos60
=-1/2