解方程(x+y)dy/dx=y-x

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解方程(x+y)dy/dx=y-x解方程(x+y)dy/dx=y-x解方程(x+y)dy/dx=y-x请参考?dy/dx=(y-x)/(y+x)=(y/x-1)/(y/x+1),设y=xu,则dy/d

解方程(x+y)dy/dx=y-x
解方程(x+y)dy/dx=y-x

解方程(x+y)dy/dx=y-x
请参考?

dy/dx=(y-x)/(y+x)=(y/x-1)/(y/x+1),
设y=xu,则dy/dx=u+xdu/dx,
∫u/(u^2+1)du+∫1/(u^2+1)du=-∫1/xdx
1/2(ln(u^2+1))+arctanu=-lnx+lnC1
ln(C1√(x^2+y^2))=-arctany/x
(x^2+y^2)=Ce^(-arctany/x)