That is a critical point. And we used the second derivative to see that this critical point is a local maximum.

这是一个临界点，考察它的二阶导数,会发现这确实是一个极大值点。

youdao

I should say that is for a function of two variables to try to decide whether a given critical point is a minimum, a maximum or a saddle point.

但这种办法并不普遍，只能用于二元函数，来判断是极小值点、极大值点还是鞍点。

youdao

And the maximum is at a critical point.

最大值点是临界点。

youdao