⑩天掌 Teaching Plan on Advanced Mathematics o 同理可证 00 00 dc-d=Q(x,y,z地 OR OR d-dztx=R(x,y,z地, ax OR a0 OP OR -)dz+( )dzdx +o )dx oz. ax ∑ ax ay 「Pa+Q+R.故有结论成立 tianjin polytechnic dmivendityTianjin Polytechnic University Teaching Plan on Advanced Mathematics dydz Q(x, y,z)dy, z Q dxdy x Q    =   −   同理可证 dzdx R(x, y,z)dz, x R dydz y R    =   −   dxdy y P x Q dzdx x R z P dydz z Q y R ( ) ( ) ( )   −   +   −   +   −       = Pdx + Qdy + Rdz.. 故有结论成立