著名数学家Ｇ·波利亚说过：“一个专心的认真备课的教师能够拿出一个有意义但又不太复杂的题目，去帮助学生发掘问题的各个方面，使得通过这道题，就好像通过一道门户，把学生引入一个完整的理论领域．”下面一道习题，因其优美简洁的结构，丰富的内涵，潜在的应用功能，... The famous mathematician G. Polya said: “A concentrating teacher who prepares lessons seriously can come up with a meaningful but not too complex topic to help students explore all aspects of the problem, so that through this question, it looks like Through a portal, the students are introduced into a complete theoretical field." The following exercise, because of its beautiful and concise structure, rich connotations, and potential application functions,...