Because the ideal “rigid joint” and “hinged joint” are inexistent, the stiffness of any connection types is between ideal rigid joint and hinged joint.

因为想节点和铰接点是不存在，任何连接形度是想接和完全铰接之间。

By using Taylor's formula, the article deduces the sufficient condition of the existent extreme value and the necessary condition of the inexistent extreme value of trinary function.

通过利用泰勒公推导出判断三元函数极值存在充分条件和极值不存在必要条件。