<em>A line of symmetry and the line between opposite points in the symmetry</em><em> are </em><u>perpendicular to each other. </u>
Explanation:
A line of simmetry splits the figure into two identical halves.
Suppose you have a symmetrical plane figure (like a square or a circle), the line of symmetry divides such figure in two sides: call them the left side and the right side.
The reflection of each point on the right side is a point on the left side along the perpendicular line that joins the two points and the line of symmetry.
For instance, if the line of symmetry is vertical, such as the x-axis, the line between the opposite points in the symmetry is horizontal, i.e. perpendicular to the x-axis (the line of summetry).
