The principle that 9 squares are equal to 15 is Sudoku, and the basic principle used is mathematical addition.

Nine squares add up to fifteen, and there are the following situations, as shown in the figure:

Jiugongge has one and only one basic solution and eight forms.

The sum of 1-9 is 45,45 ÷ 3 = 15, so the magic sum of Jiugongge =15.

Basic solution:

Exclusion method (exclusion method)

Exclusion method: using numbers to find the only space that can be filled in a cell is called exclusion method, and the only space that can be filled with numbers is called hidden list.

According to the different scope of action, elimination schemes can be divided into the following three types:

The only space that can be filled in a number is called hidden single in box in the unit of "palace", which is also called palace exclusion method.

The only space that a number can fill is called hidden single line in the "row" cell, which is also called row exclusion method.

The only space that a number can fill is called the hidden single column in the "row" cell, also known as the row exclusion method.