The first derivative will show you increase or decrease.
It’s positive or negative y’know respectively.

If the d’rivative is zero or it’s undefined,
Then that point is critical and always on your mind!

You know a saddle is a critical point,
that also is an inflection point.
You know, you know a saddle is an inflection point,
that also is a critical point.

The second d’rivative will tell you concave up or down.
Concave up, positive smile and down negative frown.

The second d’rivative is zero in between the sections,
Of concave up or down and they are called points of inflection.

You know a saddle is a critical point,
that also is an inflection point.
You know, you know a saddle is an inflection point,
that also is a critical point.
It’s a critical, it’s a critical, it’s a critical point.