For example, isosceles triangle, square, equilateral triangle, isosceles trapezoid, circle and regular polygon are all axis pairs, which are called graphs. A circle has countless symmetry axes, all of which are straight lines passing through the center of the circle.

Pay special attention to the line segment, which has two symmetry axes, one is the straight line where the line segment is located and the other is the middle vertical line of the line segment.

Extended data 1. If two graphs are symmetrical about a straight line, then the symmetry axis is the middle perpendicular of the line segment connected by any pair of corresponding points.

2. Similarly, the symmetry axis of an axisymmetric figure is the median vertical line of a line segment connected by any pair of corresponding points.

3. The distance between the point on the vertical line of the line segment and the two endpoints of the line segment is equal.

4. Symmetry axis is the set of points with equal distance to both ends of the line segment.

Baidu Encyclopedia-Axisymmetric Graphics