Fill in the blanks with rules, and let students find the simple arrangement rules of figures and numbers through observation, experiment, guessing and reasoning. In fact, the significance of finding the law to fill in the blanks lies in strengthening the understanding of the general law of sequence. Although there are many solutions, it is mainly to cultivate your ability to find the general law of series and guess the general term of series (that is, the ability to use incomplete induction), so that when you encounter some series that are difficult to find the general term by general methods, you can guess the general term formula of this series quickly and accurately through the first few terms, and then prove it by mathematical induction or reduction to absurdity or other methods to bypass the main mountain. Therefore, finding the rules to fill in the blanks will still help us to enhance our understanding of some difficulties and characteristic series.