【摘要】 讨论二元函数f(x,y)在给定点P0(x0,y0)沿一切有向直线之方向导数都存在的情形与该二元函数在P0可微的关系,并证明一个可微的充要条件.结果可推广到更多元函数的情形.更多还原

【Abstract】 This paper discusses the relationship between the differentiability of f(x,y) and the directional derivatives of f(x,y) at(x0,y0) and presents a necessary and sufficient conditionn for the differentiability of f(x,y) at(x0,y0).This result may be generized to functions of multiple variables.更多还原