1, one factor is constant, another factor is expanded several times, and the product is also expanded by the same multiple;

2, and the same, one factor is expanded several times, and the other factor is reduced by the same multiple.

"The law of product change" is the content of mathematics in the fourth grade of primary school by People's Education Press. Students' learning objectives are:

1, let students experience the discovery process of product change law, and try to express the product change law in concise language;

2. Get the general methods and experience of exploring laws and develop students' reasoning ability;

3. Cultivate students' inquiry ability, cooperation and communication ability and induction and summary ability in the learning process.