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A double-cone is a surface of revolution, generated by a line. In 3-dimensions, a surface or solid of revolution has circular symmetry around an axis, also called cylindrical symmetry or axial symmetry. An example is a right circular cone. Circular symmetry in 3 dimensions has all pyramidal symmetry, C nv as subgroups.
A circle is thus said to be symmetric under rotation or to have rotational symmetry. If the isometry is the reflection of a plane figure about a line, then the figure is said to have reflectional symmetry or line symmetry; [3] it is also possible for a figure/object to have more than one line of symmetry. [4]
The circle is a highly symmetric shape: every line through the centre forms a line of reflection symmetry, and it has rotational symmetry around the centre for every angle. Its symmetry group is the orthogonal group O(2,R). The group of rotations alone is the circle group T. All circles are similar. [12]
The type of symmetry is determined by the way the pieces are organized, or by the type of transformation: An object has reflectional symmetry (line or mirror symmetry) if there is a line (or in 3D a plane) going through it which divides it into two pieces that are mirror images of each other. [6]
There is no geometric figure that has as full symmetry group the circle group, but for a vector field it may apply (see the three-dimensional case below). the orthogonal group O(2) consisting of all rotations about a fixed point and reflections in any axis through that fixed point. This is the symmetry group of a circle.
Geometric objects with a well-defined axis include circles (any line through the center), spheres, cylinders, [2] conic sections, and surfaces of revolution. Concentric objects are often part of the broad category of whorled patterns , which also includes spirals (a curve which emanates from a point, moving farther away as it revolves around ...
For instance, given a line containing the points A and B, the midpoint of line segment AB is defined as the point C which is the projective harmonic conjugate of the point of intersection of AB and the absolute line, with respect to A and B. A conic in a projective plane that contains the two absolute points is called a circle. Since five ...
All vertices of a regular polygon lie on a common circle (the circumscribed circle); i.e., they are concyclic points. That is, a regular polygon is a cyclic polygon. Together with the property of equal-length sides, this implies that every regular polygon also has an inscribed circle or incircle that is