高数课程妥媒血课件 镭理工大理>> 00 aP a0 oP a0 aP )dxdy )dxdy ax ay D ox a ax ay Pb+Q冲+P+Q+,PbQ小 L+AB L+bc L3+CA |= AB BC AC CA P+Q+,P+Q+,P+Q小 D =fPax+ody (L1L2L3对D来说为正方向) Http://www.heut.edu.cn     −   +   −   +   −   1 2 3 ( ) ( ) ( ) D D D dxdy y P x Q dxdy y P x Q dxdy y P x Q  +  +  + = + + + + + L AB L BC L CA Pdx Qdy Pdx Qdy Pdx Qdy 1 2 3  = + L Pdx Qdy ( , ) L1, L2 L3对D来说为正方向 D1 D2 D3 L L1 L2 L3 A B C    = + + + + + L1 L2 L3 Pdx Qdy Pdx Qdy Pdx Qdy     + = = − AB BC AC CA 