The inflection point is the point where the bump changes? The tonality of both sides can be the same, as shown in the figure, the first paragraph and the second paragraph increase monotonically, and the first derivative is greater than zero.

The monotonicity on both sides of the extreme point is different, as shown in the figure, the first derivative of the second segment monotonically increases greater than zero, and the first derivative of the third segment monotonically decreases less than zero.

The inflection point has nothing to do with the first derivative (the first derivative at this point may not exist), such as y = x (1/3).

=-= Mathematical symbols are difficult to type out and write one by one.