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

因为理想的刚节点和铰点在的，任何连形式的刚度介于理想刚和完全铰的。

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元函数极值在的充分条件和极值在的必要条件。