Symmetry: Symmetry refers to the reflection movement of figures or objects to points, straight lines or planes, which are equal or equivalent in shape, size, length and arrangement, and have a one-to-one correspondence.

Concept explanation:

Mathematically, we first define a point (axis of symmetry) that is symmetrical about a straight line, then define a figure (axis of symmetry) that is symmetrical about a straight line, and finally introduce the meaning of symmetrical figure and axis of symmetry.

We can understand symmetry in this way: a figure or an object has a one-to-one correspondence in size, shape and arrangement relative to a certain point, line or surface.

Symmetry is narrowly defined as:

An object contains several equivalent parts, and the corresponding parts are equal. The operation of restoring an object without changing the distance between any two points inside it is called symmetry operation, and it is also called inversion operation in physics.

Symmetry operations mainly include: rotation, reflection, inversion, image rotation and inversion. Rotation and reflection are basically symmetrical operations. The geometric elements that complete the symmetry operation are called symmetry element, including: rotation axis, mirror surface, symmetry center, reflection axis and anti-axis. Symmetry axis and symmetry plane are basic symmetry element.