00 aP 00 oP )d+ 00 aP Ddxdy+ ax a ax ay ax a f, Pdx+@dy+, Pdx+Ody+fPdx+ody =.Pdx+d(L1.2,l2对D来说为正方向) (3)D为复连通域, o aP )dxdy D s ax dj A ++|++|+ AB BAJAFCJCE 「+」[。}(Pdx+Qd)    −  +  −  +  −  = 1 2 3 ( ) ( ) ( ) D D D dxdy yP xQ dxdy yP xQ dxdy yP xQ =  + +  + +  + L1 L2 L3 Pdx Qdy Pdx Qdy Pdx Qdy  = + L Pdx Qdy ( , ) L1,L2 L3对D来说为正方向 (3) D为复连通域, GD L3 L2 F C E L1 A 由 B (2)知   −  D dxdy yP xQ ( )      = + + + + AB L 2 BA AFC CE {    + + +  + L EC CGA} (Pdx Qdy) 3