「Pd+g+Rkz ∫P1p(,v(),o()p() +Qφ(t),y(t),o()y(t) +Rφ(t,y(t),(t)lo(t (4)两类曲线积分之间的联系 设有向平面曲线弧为L x=o(t) y=y(t) L上点(x,y)处的切线向量的方向角为ax,B, 则Pd+小-(Psa+sp)aR t t t t dt Q t t t t P t t t t Pdx Qdy Rdz [ ( ), ( ), ( )] ( )} [ ( ), ( ), ( )] ( ) { [ ( ), ( ), ( )] ( )               +  +  =  + +   (4) 两类曲线积分之间的联系： , ( ) ( )    = = y t x t L   设有向平面曲线弧为 ： L上点(x, y)处的切线向量的方向角为, ,   + =  +  L L 则 Pdx Qdy (Pcos Qcos )ds