The area of the rectangle = 1×5=5, so the side length of the square should be √5. So the rectangle is divided into four triangles and a square, the side length of the square is 1× 1, and the three sides of the four right-angled triangles are 1, 2 and √5 respectively. When doing puzzles, the square is placed in the middle, and the hypotenuse of the four right-angled triangles is the side of the big square.