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注意到d(xy)=xdy+ydx,设u=xy则,du=xdy+ydx代入原式,得
(1+u)ydx+(1+u+u²)xdy=0,由xdy=du-ydx,代入,得
(1+u)ydx+(1+u+u²)(du-ydx)=0,
即(1+u+u²)du=u²ydx,y=u/x,则(1+u+u²)du/u³=dx/x
积分,得lny-1/xy-1/(2x²y²)+c=0
(1+u)ydx+(1+u+u²)xdy=0,由xdy=du-ydx,代入,得
(1+u)ydx+(1+u+u²)(du-ydx)=0,
即(1+u+u²)du=u²ydx,y=u/x,则(1+u+u²)du/u³=dx/x
积分,得lny-1/xy-1/(2x²y²)+c=0
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