? A, for discontinuous function, Robida derivative rule is not applicable;

? B, even if it is a continuous function, Robida's derivative rule is not omnipotent and often cannot be used.

2. There are two main ways to solve infinitesimal infinitive of infinite ratio:

? A. converting infinite calculation into infinitesimal calculation;

? B, using the law of derivative of Robida.

? (The third picture, not these two methods)

3. Take the following six pictures as concrete examples, and each picture can be clicked to enlarge;

4. Please ask and answer questions.