What does e mean in mathematics?

What is the long speech of the man in front? It seems to be beside the point! ! !

To say the origin of the base e of natural logarithm, we must say Euler (leonhard euler1707-1783), a great mathematician! Because this symbol was introduced by him, he not only invented e, but also invented many mathematical symbols, such as function symbols f(x), π, e, ∑, logx, sinx, cosx, imaginary number I and so on. As for why he chose such a symbol for naming, there are two widely recognized views: one is that after four commonly used letters, such as A, B, C and D, the first letter that is not often used is E, so he naturally chose this symbol, which represents the base of natural logarithm; One is that e is the first letter of the index. Although you may suspect that the Swiss Euler is not the mother tongue of English, it is actually an index of French and German.

High school teachers often use a joke about the base e of natural logarithm to help students remember a very special differential formula: in a mental hospital, a patient says to others all day, "I differentiate you, I differentiate you." For some reason, these patients all have a simple concept of calculus. They always think that one day they will be differentiated into zero and disappear like ordinary polynomial functions, so they avoid him. However, one day he met an unmoved person, and he was surprised. This person simply said to him, "I am the x power of E". The differential formula is: No matter how many times E differentiates X, the result is still E! No wonder math students use e to describe unswerving love!