Explain mathematically why the bottom of yurts is round, and the cross sections of roots and stems of most plants are also round.

Mongolian yurts are closed and need to consume materials.

When the perimeter is constant, the area of the circle is the largest. Therefore, using the same amount of cloth in a circle can maximize the internal space.

In addition, there may be strong winds on the grassland, and the influence of the wind can be minimized by using circles. If it is square and the wind blows directly to one side, the building will bear great stress. Obviously, the stability factor should also be considered when tying yurts on the grassland.

As for plants, the same is true for roots to absorb and transmit nutrients and water. And is more flexible than other shapes.

Well, actually, after the plant is born, I think, what should my roots and stems look like? After thinking about it, it doesn't know it. Forget it. It grows a little in all directions and becomes a circle. . . )