x=cosa/(1+cosa),y=sina/(1+cosa)的普通参数方程

x=cosa/(1+cosa)x+xcosa=cosacosa=x/(1-x)y=sina/(1+cosa)y+ycosa=sinay+xy/(1-x)=sinay/(1-x)=sina(sina)^2+(cosa)^2=1[x/(1-x)]^2+[y/(1-x)]^2=1x^2+y^2=(1-x)^2y^2=-2x+1