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^2
x+xt^2-3t^2=0
x+t^2(x-3)=0
t^2(x-3)=-x
t^2=-x/(x-3)
y=(5-t^2)/(1+t^2)
y(1+t^2)=5-t^2
y+yt^2=5-t^2
yt^2+t^2=5-y
t^2(y+1)=5-y
t^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+3y
6x+3y-15=0
2x+y-5=0