tgπ/4=1所以tg(π/4+a)=(1+tga)/(1-tga)=1/22+2tga=1-tgatga=-1/3sina/cosa=tga=-1/3cosa=-3sina代入恒等式(sina)^2+(cosa)^2=1所以(sina)^2=1/10(cosa)^2=9/10sina/cosa=-1/3