The sum of (1)9 numbers is 9 times of the median number; Agree to other boxes; If a stands for the middle number, then the sum of 9 numbers is 9a; This is true for any month's calendar, because these nine numbers can be expressed by an algebraic expression with the same letter, with A in the middle, so the nine numbers in the box are arranged as follows.

a-8 a-7 a-6

a- 1

A+6 a+7 a+8, the result of adding these nine algebraic expressions is 9 A; The number difference of each row is 1, the number difference of each column is 7, and so on.

(2) This is the same as the last one, with row difference 1 and column difference of 7.

This is mainly to let students observe the law between numbers and express it with algebraic expressions.