I come from Ningbo, Zhejiang. Although derivative is an optional course, it is an important tool or idea to understand functions.

However, if you want to get high marks in mathematics in the college entrance examination, it is of course beneficial to learn derivatives by yourself;

Our teacher teaches mathematics even if he takes elective courses;

Because derivatives are really useful for solving problems (conic curves and functions), you can use derivatives to quickly solve some choices and fill in the blanks, which is a good way to understand functions and understand limits; Derivative is also the basis of higher mathematics and differentiation in colleges and universities;

I know a god of learning, who read popular science books in junior high school and already knows derivatives;

Finally, I think to learn math well, we really need to think about some difficult problems. Solving a difficult problem is often greater than doing many similar problems.

This is just my personal opinion.