2)设=()n=0(xy,3)/与均可微求 解令v=xy,w Z一L 则=f() x dx f(u) )=f(n)(y01+-2) ay ax aw ax oy(ur'oysf'(a Ou Ov ou Ow az f(u) (xo12 z v w u y , , x x v xy w y 解 令 = = ( ) ( ) u v u w f u v x w x     =   +       ( ) z u f u x x   =     则 1 2 1 f u y ( ) ( ); y =  +      (2) ( ), ( , ), , . x z f u u xy f dz y 设 与 均可微 求 = =  ( ) z u f u y y   =     ( ) ( ) u v u w f u v y w y     =   +       1 2 2 1 f u x ( ) ( ); y =  −     