问题 选择题 若sin(π+α)=12,32π<α<2π,则cos(2π-α)的值是( )A.32B.12C.-32D.±32 答案 ∵sin(π+α)=12,32π<α<2π,∴sinα=-12而cos(2π-α)=cosα,32π<α<2π,∴cosα=32故选A.