One more way.
Just do an experiment. Draw a square and some rectangles of different length and breadth, on a piece of paper. Bisect the respective square and rectangles by drawing a diagonal line, and measure the angles.
And then just let me know the angles.
Only square will have 45 degree angle (both), while all the rectangles (unless it is square, as IMO square is also a type of rectangle) will have different angles, according to their length and breadth ratio.
Good night
PS
Even other traders, who are in line with Somatung, can perform this experiment and report their conclusion, here.