(sinα+cosα)/(sinα-cosα)=2sinα+cosα=2sinα-2cosαsinα=3cosα(sinα)^2+(cosα)^2=1所以(cosα)^2=1/10(sinα)^2=9/10因为sinα=3cosα所以sinα和cosα同号sinα*cosα>0所以sinα*cosα=根号(sinα)^2*(c...