Is L'H?pital's Law in high school? You shouldn't take the college entrance examination, and you can't understand the example you gave. Write them down on paper and let's discuss them together. Here, let me explain L'H?pital's law to you first:

L'H?pital's law is a method to find the limit of indefinite formula, which can be divided into "0/0" and "infinity/infinity" (if not, it will be transformed into these two). The law of Lobida is to derive the numerator and denominator of this indefinite form at the same time. If the limit of the derivative exists, then the limit of the original function also exists and is equal! The proof method is as follows: (suppose the independent variable X tends to a certain value A, the molecular function is F, the denominator is F, the derivative of F exists, and the derivative of F is not 0).

Since the limit of f/F has nothing to do with f f when x tends to a, it can be assumed that f(a)=F(a)=0.

So f f is continuous in a certain domain of a.

Let x be a point in this domain, then on the interval with xèa as the endpoint, it is obtained by Cauchy mean value theorem:

F/f = [f (x)-f (a)]/[f (x)-f (a)] = f "(e)/f" (e) (e is between x and a) is proof.