# In calculus, which questions can the naive ask that the learned cannot answer?

Number theory is known to be a field in which many questions that can be understood by secondary-school pupils have defied the most formidable mathematicians’ attempts to answer them.

Calculus is not known to be such a field, as far as I know. (For now, let’s just assume this means the basic topics included in the staid and stagnant conventional first-year calculus course.)

What are

1. the most prominent and

questions that can be understood by those who know the concepts taught in first-year calculus and whose solutions are unknown?

I’m not looking for problems that people who know only first-year calculus can solve, but only for questions that they can understand. It would be acceptable to include questions that can be understood only in a somewhat less than logically rigorous way by students at that level.

2) Closely related (although $\liminf$ is typically not covered in first year calculus courses, it’s too not much of a stretch): whether or not