(y^3+xy^2+y)dx+(x^3+x^2y+x)dy=0
(x+y)(x^2dy+y^2dx)+dxy=0
(1/x+1/y)(x^2dy+y^2dx)+d(xy)/xy=0
(1+1/xy)dxy+[y^2/x]dx+[x^2/y]dy=0
(1/x^2y^2+1/x^3y^3)dxy+dx/x^3+dy/y^3=0
2xy+1+y^2+x^2=cx^2y^2
(x+y)^2+1=cx^2y^2
有時就是需要一些神來一筆，才有辦法找到曙光啊

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