Question

cos195°的值為（　�。�

A． 6 + 2 4

B．- 6 + 2 4

C． 6 - 2 4

D． 2 - 6 4

Answer 1

cos195°=cos（180°+15°）=-cos15°=-cos（45°-30°）=-

2

2

×

3

2

-

2

2

×

1

2

=-

6 + 2

4

．
故選B