探讨二元函数的连续性、偏导数、方向导数以及可微性之间的关系，有助于我们对二元函数的学习。

A discussion of the relations between continuity, partial derivative, directional derivative and differentiability of binary function is helpful for us to study binary function.

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然后利用正切锥方向导数定义一类正切锥F 凸函数类，并给出了（VP）正切锥真有效解的充分性条件；

Then, we define a class of tangent cone F convexity in terms of the tangent cone directional derivative, and prove the sufficient optimality conditions for (VP).

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多元函数的连续性，偏导数，方向导数及可微性之间的关系。

The Relation between the Continuity, the Partial Derivatives, the Directional Derivatives and the Differentiability of a Function.

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