提示：z=f(x+y+z,xyz) -斤-原片0g+ &x e”+6 8x 1-f-xyf .1=f(+1 xxy) 1-f-xyf Oz f+yzf2 ·0(商0(r Ox f+x红分 8y f'+yzfz x   = = 提示: z = f (x + y + z, xyz) =   x z 1 f  ( ) x z    1+ 2 + f  ( ) x z yz xy    + x z   1 2 f + yzf  1 1 2 − f − xy f  • 1= 1 f  ( +1)    z x 2 + f  ( xy ) z x yz +   •  1 1 2 − f − xy f  1 2 f + yzf  y x   = − 0 = 1 f  ( +1)    y x 2 + f  ( xz ) y x yz +   •  1 2 f + xzf  1 2 f + yzf 