Question

若cos(-100°)=a,则tan80°等于(    )

A.-           B.           C.-            D.

Answer 1

解析:∵cos(-100°)=cos100°=a,

∴cos100°=cos(180°-80°)=-cos80°=a,

即cos80°=-a,sin80°=.

∴tan80°==-.

答案:A