This is a special shape. It looks beautiful. It is widely used in daily life, such as bracelets, donuts, bagels, hula hoops, tire linings and so on.

A circle C has a straight line on its plane that does not intersect it as an axis. This is the torus.

The mother circle of the torus is either of the two circles cut by its axis plane, that is, the circle C that was originally rotated.

The surface of the torus is the torus, and the area formula is

S=4π？ Rr=(2πR)×(2πr)，

The volume of the torus is

V=π？ Rr？ =(2πR)×(πr？ ),

Where r is the distance from the center of the mother circle c to the axis, and r is the radius of the mother circle C.

2πr can be regarded as the rotation distance of the mother circle C, 2πR is the circumference of the circle C, πR? Is the area of circle C.