Please see, the red triangle in the picture above and the green triangle and the big triangle in the picture below should be similar triangles, but they are not. Let me calculate for you: the two right-angled sides of the red triangle are the two right-angled sides of the big triangle, and 8 to 13 is not equal to 3 to 5, so the red triangle and the big triangle are not similar triangles;
Green triangle: 5 13 is not equal to 2/5. So the green triangle and the big triangle are not similar triangles. There is no problem with the right-angled sides of the red-green triangle and the big triangle, so it can be concluded from the above points that the problem should be on the hypotenuse.
The hypotenuse of the big triangle formed by the hypotenuse of the red-green triangle is not a straight line, but the inflection point at the joint of the hypotenuse of the red-green triangle. The angle of this inflection point changes because of the change of the position of the red-green triangle. At this time, you should know that the upper and lower triangles are actually two quadrilaterals. In the above figure, the angle of inflection point is greater than 180 degrees and less than 360 degrees, which is geometrically called the optimal angle, and in the following figure, it is less than 180 degrees and greater than 90 degrees, which is geometrically called the obtuse angle.
To put it bluntly, the hypotenuse in the upper picture is concave and the hypotenuse in the lower picture is convex. If you overlap the two pictures, you will find that the hypotenuse of the two pictures will not overlap, and the area of the middle part of the two hypotenuse is the area of the missing square in the picture below.
You got it? I feel dizzy.