刚学积分,帮忙求一道一元微分方程.
1个回答

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.