⑩天掌 Teaching Plan on Advanced Mathematics o 00 oP 两式相加得 h=Px+Q小 证明(2) 若区域D由按段光 滑的闭曲线围成如图, 将D分成三个既是X一型又是 Y-型的区域D1,D2,D3 00 aP 00 aP )dxdy ax a D,+, +D, ax g dta tianjin polytechnic dmivendityTianjin Polytechnic University Teaching Plan on Advanced Mathematics 若区域D由按段光 滑的闭曲线围成.如图, 证明(2) L L1 L2 L3 D D1 D2 D3 两式相加得   = +   −   L D dxdy Pdx Qdy y P x Q ( ) 将D分成三个既是X −型又是 Y −型的区域D1 ,D2 ,D3 .   + +   −   =   −   1 2 3 ( ) ( ) D D D D dxdy y P x Q dxdy y P x Q