∵(sinα)^2+(cosα)^2=1,∴cosα=√[1-(sinα)^2]=√[1-(1/3)^2]=2√2/3,∵α是第二象限角,∴cosα<0,∴tanα=sinα/cosα=-(1/3)/(2√2/3)=-√2/4.
a是第二象限角,cosa<0,cosa=根号(1-1/9)=-2根2/3tana=sina/cosa=-根2/4
