⑩天掌 Teaching Plan on Advanced Mathematics o 例2设x2+ 4z=0,求 解令F(x,y,z)=x2+y2+x-4x, 则F=2x,F2=2z z ax F 2-z az (2-z)+x(2-x)+x ax ax (2-z) (2 3 (2-z)2+ tianjin polytechnic dmivendityTianjin Polytechnic University Teaching Plan on Advanced Mathematics 解 令 则 ( , , ) 4 , 2 2 2 F x y z = x + y + z - z F 2x, x = F = 2z - 4, z , 2 z x F F x z z x - = - =   2 2 x z   2 (2 ) (2 ) z x z z x -   - + = 2 (2 ) 2 (2 ) z z x z x - - - +  = . (2 ) (2 ) 3 2 2 z z x - - + = 例2 设 4 0 2 2 2 x + y + z - z = ，求 2 2 x z  