1.cos(-420°)的值等于( ) a.32 b.-32 c.12 d.-12 解析:选c.cos(-420°)=cos(360°+60°)=cos 60°=12. 2.sin2(2π-α)+cos(π+α)•cos(π-α)+1的值是( ) a.1 b.2 c.0 d.2sin2α 解析:选b.原式=sin2α+cos α•cos α+1=1+1=2. 3.已知cos α=35,则sin(3π+α)•cos(2π-α)•tan(π-α)等于( ) a.±35 b.±45 c.925 d.1625