The word "Rule" comes from the English word "rule" and has two meanings:

1, the essence of the theorem, but the essence is the calculation method:

Such as sine law = sine theorem, cosine law = cosine theorem.

Derivation of product rules = product;

Quotation rule = derivation of quotient;

Chain rule = derivative method of compound function (chain derivative method).

Pythagorean theorem is not a rule, but a theorem, "Pythagorean theorem"

2. Judgment method and simplified calculation method:

For example, Robida's Law = Robida's Law.

Robida's law itself cannot be used to calculate the limit, but it is used in seven infinitives.

You can change the infinitive into a definite form, and then calculate the limit value by other methods.

Therefore, Robida's law cannot judge infinitives, but can only change infinitives into definite ones.

What we usually call quadratic function discriminant is not a rule in English, but a special vocabulary.

Discriminatory formula.