Jiugongge equals the sum of all three numbers in the diagonal of 3, 5,-7, 1, 7,-3, 9,-5 and-1.

These nine numbers are arranged in descending order:-7,-5,-3,-1, 1, 3, 5, 7, 9.

1 is a median and an average, so it should be in the middle.

the sum of other numbers paired from beginning to end is 2, so they are matched at both ends of 1.

and make the sum of three numbers on four sides of the nine-square grid 1+2=3.

in this way, 9 and -7 can only be matched in the middle, not in the corner.

Similar 7 and -5 can only be allocated in the other two intermediate positions.

tentative combination, easy to get the result:

-5 9 -1

5 1 -3

3 -7 7

form:

connect the equivalent formulas (or numbers represented by letters) by "=".

equations are divided into equations with unknowns and equations without unknowns.

For example:

x+1 = 3-an equation with unknowns;

2+1 = 3-an equation without unknowns.

it should be noted that some equations with unknowns have no solutions, but they are still equations, for example, x+1 = x-x has no solutions.