What is a reflecting line in geometry?

A reflecting line, often referred to as a line of symmetry or a mirror line, is defined as a line that creates a mirror image of a shape across it. When a geometric figure is reflected over this line, every point on the shape is mapped to a corresponding point on the other side of the line at an equal distance from the line itself. This concept is significant in geometry as it relates to symmetries, transformations, and understanding how shapes interact in space.

For example, if a triangle is reflected across a line, the reflected triangle will have the same size and shape but will be positioned on the opposite side of the line, showcasing symmetry. The idea of reflection is widely used in applications involving design, art, and physics, particularly in understanding how light interacts with surfaces.

The other options describe different geometric concepts but do not capture the essence of what a reflecting line specifically does in relation to those shapes.