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.

通过利用泰勒公式推导出判断三极值存在的充分条件极值不存在的必要条件。

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

理想的刚节点铰接点是不存在的，任何连接形式的刚度都是介于理想刚接完全铰接之间的。