令y=xu
则y'=u+xu'
代入原方程得:
u+xu'=(u^2-2u-1)/(u^2+2u-1)
xu'=(u^2-2u-1)/(u^2+2u-1)-u
xdu/dx=-(u+1+u^3+u^2)/(u^2+2u-1)
du*(u^2+2u-1)/(u^3+u^2+u+1)=-dx/x
du*(u^2+2u-1)/[(u+1)(u^2+1)]=-dx/x
du*[ -1/(u+1)+2u/(u^2+1)]=-dx/x
积分:-ln|u+1|+ln(u^2+1)=-ln|x|+C1
(u^2+1)/(u+1)=c/x
即(y^2/x^2+1)/(y/x+1)=c/x
化简为:y^2+x^2=c(y+x)
这是圆的方程.