且P(x)+(x,y ={Po(,w(O)p()+g0woy(o)t 特殊情形 (1)L:y=y(x)x起点为a,终点为b 牛则Pd+Q=Px,yx)+2xy(x)y(x) A(2)L:x=x(y)点为c,终点为d 王则P+2b-Px0(0+xP 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 + =  +