角a的终边落在直线上y=2x上,则设直线上一点P(m,2m),(m不=0) 所以,OP=根号(m^2+4m^2)=根号5 *|m| (1)当m>0时,sina=y/OP=2m/(根号5 m)=2根号5/5 (2)当m<0时,sina=y/OP=2m/(-根号5 m)=-2根号5/5
