且』P(x,d+(x,y)d ={Plo(.(o)lp()+gp(y(o)()t 特殊情形 (1)L:y=y(x)x起点为a,终点为b 牛则P+h=Pxy(+x((k (2)L:x=x(y)点为e,终点为d JI, Pdx+ody=(PIx(), ylx'(y)+Q(x(y), yl)dyP t t t Q t t t dt P x y dx Q x y dy L { [ ( ), ( )] ( ) [ ( ), ( )] ( )} ( , ) ( , )         =  +  +  且 特殊情形 (1) L : y = y(x) x起点为a，终点为b. Pdx Qdy {P[x, y(x)] Q[x, y(x)]y (x)}dx. b L a 则 + = +  (2) L : x = x( y) y起点为c，终点为d. Pdx Qdy {P[x( y), y]x ( y) Q[x( y), y]}dy. d L c 则 + =  +