tanα=sinα/cosα=2,sinα=2cosα;(sinα)^2+(cosα)^2=1,(2cosα)^2+(cosα)^2=1,5(cosα)^2=1,cosα=±1/5√5；2sinα-cosαsinα+2cosα=2*2cosα-cosα*2cosα+2cosα=6cosα-2(cosα)^2=-2/5±6/5√5