Proof: The derivative of 𝑒ˣ is 𝑒ˣ

$e^x$‍ is the only function that is the derivative of itself!

(Well, actually, $f(x)=0$‍ is also the derivative of itself, but it's not a very interesting function...)

The AP Calculus course doesn't require knowing the proof of this fact, but we believe that as long as a proof is accessible, there's always something to learn from it. In general, it's always good to require some kind of proof or justification for the theorems you learn.