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Dy yDx

解:∵(y+x)dy-ydx=0 ==>ydy+xdy-ydx=0 ==>dy/y-(ydx-xdy)/y^2=0 (等式两端同除y^2) ==>dy/y-d(x/y)=0 ==>∫dy/y-∫d(x/y)=0 ==>ln│y│-x/y=ln│C│ (C是积分常数) ==>ye^(-x/y)=C ==>y=Ce^(x/y) ∴原方程的通解是y=Ce^(x/y)。

用格林公式:奇点(0,0)不在积分域内. I = ∮L (ydx - xdy)/(x^2 + y^2) = ∫∫D [(x^2 - y^2)/(x^2 + y^2)^2 - (x^2 - y^2)/(x^2 + y^2)^2] dxdy = 0 用参数方程. { x = 1 + cost、dx = - sint dt { y = 1 + sint、dy = cost dt 0 ≤ t ≤ 2π ∮L (ydx...

详细步骤写在纸上了

解:∵(x+y)dy–ydx=0 ==>ydy-(ydx-xdy)=0 ==>dy/y-(ydx-xdy)/y^2=0 (等式两端同除y^2) ==>dy/y-d(x/y)=0 ==>ln│y│-x/y=ln│C│ (C是常数) ==>ye^(-x/y)=C ==>y=Ce^(x/y) ∴原方程的通解是y=Ce^(x/y)。

解:∵(2x-y^2)dy-ydx=0 ==>ydx-2xdy+y^2dy=0 ==>(ydx-2xdy)/y^3+dy/y=0 (等式两端同除y^3) ==>∫(ydx-2xdy)/y^3+∫dy/y=0 ==>x/y^2+ln│y│=C (C是积分常数) ==>x=(C-ln│y│)y^2 ∴此方程的通解是x=(C-ln│y│)y^2。

解:∵(y^2-6x)dy+2ydx=0 ==>dy/y^2-6xdy/y^4+2dx/y^3=0 (等式两端同除y^4) ==>-d(1/y)+d(2x/y^3)=0 ==>-∫d(1/y)+∫d(2x/y^3)=0 ==>-1/y+2x/y^3=C/2 (C是积分常数) ==>x=Cy^3+y^2/2 ∴此方程的通解是x=Cy^3+y^2/2。

∫2ydx+2xdy=∫2 d(xy)=2xy+C

有个简单的解法: xdy-ydx=y^2dy变形:(xdy-ydx)/y^2=dy 由于:d(x/y)=(ydx-xdy)/y^2 故:d(x/y)=-dy 通解为:x/y=-y+C 或:x=y(C-y)

大概是这样

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