The nine numbers 1-9 are listed in three formulas. The sum of horizontal, vertical and oblique directions should be equal to 15. How to calculate? Is there any rule?

The nine numbers 1-9 are listed in three formulas. The sum of horizontal, vertical and oblique directions should be equal to 15. How to calculate? Is there any rule?

6 1 8
7 5 3
2 9 4
The middle one must be the middle one of the numbers listed, such as 5, 1 and 9 above. Don't put them in the four corners. Let's follow the others

How does 3388 add up to 24

8÷(3-8÷3)=24

-1,3, - 5,7, - 9,11, - 13... According to this rule, how many numbers do you need to add up to make the sum equal to 0
-1, - 5, - 9,11, - 13... According to this rule, how many numbers do you need to add up to make the sum equal to 0? Write a correct formula

It is estimated that it will never be zero, because the following positive numbers are larger than the previous negative numbers, so the sum of them will always be positive