The bottom surface of the cylinder, cone, and round table are all round. Is that right?

I've also encountered this question, and I judged it right, but it turned out to be wrong, and the teacher told me that it was a face.

The concept of a circle in mathematics: an arc enclosed around a point is called a circle. That is, a circle is a circle of lines.

The above three three-dimensional figures are made up of faces. Lines are not polygons. The statement of this question can only be said to be not rigorous, just like taking the straight line where the diameter of the semicircle is located as the axis of rotation, and the rotating body formed by the rotation of the semicircular surface is a sphere, if it is not said to be a semicircular surface here, then it is wrong, thinking that if it is said to be a semicircle, then the rotation is a circle, which is hollow and not solid, then it is not a sphere.

Similarly, a circle refers to a circle, not a face.

The concept of a circle in mathematics: an arc enclosed around a point is called a circle. That is, a circle is a circle of lines.

The above three three-dimensional figures are made up of faces. Lines are not polygons. The statement of this question can only be said to be not rigorous, just like taking the straight line where the diameter of the semicircle is located as the axis of rotation, and the rotating body formed by the rotation of the semicircular surface is a sphere, if it is not said to be a semicircular surface here, then it is wrong, thinking that if it is said to be a semicircle, then the rotation is a circle, which is hollow and not solid, then it is not a sphere.

Similarly, a circle refers to a circle, not a face.

The statement of this question can only be said to be not rigorous, just like taking the straight line where the diameter of the semicircle is located as the axis of rotation, and the rotating body formed by the rotation of the semicircular surface is a sphere, if it is not said to be a semicircular surface here, then it is wrong, thinking that if it is said to be a semicircle, then the rotation is a circle, which is hollow and not solid, then it is not a sphere. Similarly, a circle refers to a circle, not a face.

False, the statement of the circle is not rigorous, since it is geometry, then it is composed of faces, so the correct statement should be a circle surface.

The analysis process is as follows:

A circle is a curve, a boundary, and a circle is a surface, a region. The bottom surface of both the cylinder and the cone have one face, so the bottom surface of the cylinder and the round digging ridge cone are both rounded.

The statement that every side of a cylinder is a circle is not true. There is a fixed line and a moving line in the same plane, when the plane of the stool vertical rotates around this fixed line, the surface formed by this moving line is called the rotating surface, this fixed line is called the axis of the rotating surface, and this moving line is called the bus bar of the rotating surface. If the bus is a straight line parallel to the axis, then the resulting rotating surface is called a cylindrical surface.

If the cylindrical surface is truncated by two planes perpendicular to the axis, then the geometry enclosed by the two thick sections and the cylindrical surface is called a straight cylinder.

Abbreviated as a cylinder. The two identical round surfaces of a cylinder are called the bottom surface (which is divided into upper bottom and lower bottom); The cylinder has a curved surface, called the side; The distance between the corresponding points of the two bottom surfaces is called the high (there are countless lines of height).

Features: 1. The bottom surface of the cylinder is a circle, and in the same cylinder, the size of the circle is the same.

2. The distance between the two sides of the cylinder is called high, and the side of the cylinder is opened to obtain a rectangle, and the length of this rectangle is the bottom perimeter of the cylinder.

Folded round liter large column base area:

The base area of the cylinder = r 2;

Folded cylindrical surface area:

The surface area of the cylinder = side area + two base areas;

Cylindrical surface area, bottom circumference* (height + radius);

S-bar table = 2 r(r+h).

Right. Since it is called "cone" and "cylinder", of course, the bottom surface is round, otherwise it is called "square column" and "prism".

That's right. Both the cylinder and the bottom of the cone are circles.

The cylinder with different upper and lower bottom areas is called the round table.

The volume of the round table is auspicious and sliding:

where r'is the upper bottom radius, and r is the lower bottom radius.

The round table can also be thought of as the part of the cone that is cut off by the two perpendicular combustion planes of its axis, so it can also be called a "truncated cone".

Reference.

There may be two undersides here. That is, the circle you see below, and the upper side it is on.

Then if it's a cylinder, it's round on both sides, correct.

Cone: The bottom is a circle, the top is pointed, and the bottom surface should be said to be a circle with a little in the middle, it is not a circle.

The same is true for the round table, the bottom surface of the large side is a circle, and the bottom surface of the small side should be two concentric circles.

Cylinders, cones, and spheres are grouped based on the fact that they have at least one surface

Therefore, d