This puzzle is part of the Monthly Topic Challenge #14: Think inside the (very small) box!.
Place the digits 1 to 9 in the box below in such a way that in each row, each column and each diagonal, one of the numbers is the sum of the two others.
- Combining digits is not allowed. Put one digit in each cell.
- Rotations and symmetries don't make a difference.
- The digits in the image are there for illustration purpose. Ignore them.
While this task might look impossible at first, think harder.
Taken at face value the task is indeed impossible. You need to rely on some lateral thinking. Almost cheating.
My apologies for that.
(this is my own creation)