Pull the hypotenuse of the left triangle to the upper left corner and the hypotenuse of the right triangle to the upper right corner until a square is formed. Or: make a vertical line to the two hypotenuses through the middle vertical foot to form a small square, and then pull the small triangles on the left and right sides into this small square to hide.
Decision theorem
1: A diamond with equal diagonal lines is a square.
2. Diamonds with right angles are squares.
3: Rectangles with diagonal lines perpendicular to each other are squares.
4. A set of rectangles with equal adjacent sides is a square.
5. A set of parallelograms with equal adjacent sides and one angle at right angles is a square.
Reference to the above content: Baidu Encyclopedia-Plaza