The barrel is not a cylinder, but a platform. The cylinder is composed of two bottoms and one side. A cylinder has two parallel lines, a fixed line and a moving line in the same plane. When the plane rotates around the fixed line for one week, the geometry surrounded by two sections and rotating surfaces is called a cylinder, that is, a cylinder. So the barrel is not a cylinder.

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A plane parallel to the bottom of the cone is used to cut the cone. The part between the bottom and the section is called the circular platform. Like the cylinder and cone, the circular platform also has axis, bottom, side and bus, and the circular platform is represented by the letter of the axis of the circular platform. The geometry surrounded by the curved surface formed by the rotation of the other sides is called a circular platform. The axis of rotation is called the axis of the circular table.

The circular surface formed by the rotation of the upper and lower bottoms of the right angle trapezoid is called the upper and lower bottoms of the round table, the curved surface formed by the rotation of the other waist is called the side of the round table, the waist of the right angle trapezoid at each position on the side is called the bus of the round table, the length of the waist of the trapezoid on the axis of the round table is called the height of the round table, and the height of the round table is also the distance between the upper and lower bottoms. The frustum can also be considered as the part of the cone cut by the two vertical planes of its axis, so it can also be called "truncated cone".