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

因为理想刚节点和点是不，任何连形式刚度是介于理想刚和完之间。

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.

通过利用泰勒公式推导出判断三元函数极值充分条件和极值不必要条件。