dy/dx-3y/x=x^4用常数变易法~先算：dy/dx-3y/x=0即：dy/dx=3y/xdy/y=3*dx/x∫ dy/y=3*∫ dx/xlny=3*lnx+c1y=Cx^3令C=C(x)dy/dx=C'x^3+3Cx^2于是回代：dy/dx-3y/x=x^4C'x^3+3Cx^2-3Cx^2=x^4C'=xC=x^2/2+c2于是,y=x^3(...