记为∫(P)=lim∑f(P)As →>0 S (1)若S=L,f(P)=f(x,y),则 ∫f(x,y)ds=lim∑f(5,n)△s ->0 平面曲线上对弧长的曲线积分 (2)若S=I,∫(P)=f(x,y,z),则 ∫f(x,y,z)ds=lm∑f(5,7,5)△s 空间曲线上对弧长的曲线积分记为 ( ) lim ( ) . 1 0   → = =  n i i i S f P ds f P s  (1) 若S = L, f (P) = f (x, y),则 ( , ) lim ( , ) . 1 0   → = =  n i i i i L f x y ds f   s  —平面曲线上对弧长的曲线积分 (2) 若S = , f (P) = f (x, y,z),则 ( , , ) lim ( , , ) . 1 0    → = =  n i i i i i f x y z ds f    s  —空间曲线上对弧长的曲线积分