1, the center of the line segment is the midpoint of the line segment,

2. The center of a plane figure means that only figures with symmetrical centers have centers.

The so-called central symmetry is defined in this way. If any point on the graph and the symmetrical point of the point are still on the graph, the graph forms a central symmetric graph, which is called the symmetric center of the graph. If the center of the circle is a square or rectangle.

3. The center of a triangle is an alternative concept. A triangle has no center of symmetry, and a regular triangle has no center of symmetry. Because people are used to it, the center of a triangle actually means that when the inscribed circle and the circumscribed circle coincide, that is, the center of a regular triangle, the outer center recombines what "center" means that the triangle is not a centrally symmetrical figure.

Cubes, cuboids and spheres are all centrally symmetric figures;