dy/dx-y/x=x^2xdy-ydx=x^3dx由d(y/x)=(xdy-ydx)/x^2得到d(y/x)=xdx=d(x^2)/2即d(y/x-(1/2)x^2)=0y/x-(1/2)x^2=Cy=x(C+(1/2)x^2)
