cos(π+α)=1/2,且sin2α>0,则sinα=?

∵cos(π+α)=1/2∴cosα=-1/2∵sin2α=2sinαcosα>0∴sinα＜0∴sinα=-根号(1-cos^2α) = -根号(1-(-1/2)^2) = -根号3 /2