a为第二象限角,则 cosa＜0 而sina+cosa=1,所以 cosa=-√(1-sina)=-√[1-(3/5)]=-4/5 则tana=sina/cosa=(3/5)/(-4/5)=-3/4 则tan(a+π/4)=(tana+tanπ/4)/(1-tana*tanπ/4)=(-3/4+1)/[1-(-3/4)*1]=(1/4)/(7/4)=1/7 所...