曲线{x=3t^2/(1+t^2) y=(5-t^2)/(1+t^2) (t为参数）的普通方程是

x=3t^2/(1+t^2)x(1+t^2)=3t^2x+xt^2-3t^2=0x+t^2(x-3)=0t^2(x-3)=-xt^2=-x/(x-3)y=(5-t^2)/(1+t^2)y(1+t^2)=5-t^2y+yt^2=5-t^2yt^2+t^2=5-yt^2(y+1)=5-yt^2=(5-y)/(y+1)(5-y)/(y+1)=-x/(x-3)-xy-x=(5-y)(x-3)-xy-x=5x-15-xy+3y-x=5x-15+3y6x+3y-15=02x+y-5=0