(2)L:x=φ(y)c≤y≤d. 生』x)=no)y+90 2(y)y (c<d) 推广:r:x=φ(t),y=y(t),z=o(t).(a≤t≤B f(x, y, z)ds B flo(t),y(t),o(tl2(t)+y2(t)+@2(t)dt (a<B) 上页 圆推广:  : x = (t), y =(t), z =(t). (  t   ) ( ) [ ( ), ( ), ( )] ( ) ( ) ( ) ( , , ) 2 2 2            =  +  +    f t t t t t t dt f x y z ds (2) L : x = ( y) c  y  d. ( , ) [ ( ), ] 1 ( ) . 2 f x y ds f y y y dy d L c =  +  (c  d )