1. Fold the chart along a straight line. If the parts on both sides of a straight line can completely overlap, then this graph is called an axisymmetric graph. This straight line is its axis of symmetry. At this time, we also say that this figure is symmetrical about this straight line (axis).

2. Fold the chart along a straight line. If it can completely coincide with another figure, the two figures are said to be symmetrical about this line. This straight line is called the axis of symmetry. The overlapping points after folding are the corresponding points, which are called symmetrical points.

3. The difference and connection between axisymmetric graphics and axisymmetric graphics.

4. The essence of axial symmetry: Two figures symmetrical about a straight line are conformal. If two figures 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. The symmetry axis of an axisymmetric figure is the perpendicular bisector of a line segment connected by any pair of corresponding points. If the straight line connecting the corresponding points of two graphs is vertically bisected by the same straight line, the two graphs are symmetrical about this straight line.

5. A straight line passing through the midpoint of a line segment and perpendicular to this line segment is called the median line of this line segment, also called the median line.

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

7. The points with the same distance between the two ends of the line segment are on the middle vertical line of the line segment: in the plane rectangular coordinate system, the horizontal coordinates of the points symmetrical about the X axis are equal, but the vertical coordinates are opposite. The horizontal coordinates of points symmetrical about the Y axis are opposite to each other, and the vertical coordinates are equal.

8. The perpendicular lines of the three sides of a triangle intersect at a point, and the distance from the point to the three vertices of the triangle is equal.