tanα=1/2,,2sinα=cosα 4sin^2α=cos^2α=1-sin^2α ,sin^2α=1/5 ,cos^2α=4/5（1）sinα=-√5/5（2）(sinα+2cosα)/(-sinα+cosα)=(sinα+4sinα)/(-sinα+2sinα)=5（3）1/-sin^2（α)+2cos^2（α)=-5+8/5=-1...