设x+y+z-e-(x+y+z)=0，x+y+z≠0，则等∂2z/∂2z=______．

设x+y+z-e^-(x+y+z)=0，x+y+z≠0，则等∂²z/∂²z=______．
【正确答案】：由1+∂z/∂x+e^-(x+y+z)(1+∂z/∂x)=0，得∂z/∂x=-1，故∂²z/∂x²=0．

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设x+y+z-e-(x+y+z)=0，x+y+z≠0，则等&#8706;2z/&#8706;2z=______．