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

因为理想的刚铰接是不存在的，任何连接形式的刚度是介于理想刚接完全铰接之间的。

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.

通过勒公式推导出判断三元函数极值存在的充分条件极值不存在的必要条件。