A shape can be reflected across a line of reflection to create an image.
The line of reflection is also called the mirror line.
The triangle PQR has been reflected in the mirror line to create the image P'Q'R'.
Reflection is an example of a transformation. A transformation is a way of changing the size or position of a shape.
Every point in the image is the same distance from the mirror line as the original shape.
The line joining a point on the original shape to the same point on the image is perpendicular to the mirror line.
For example, the line between R and R' is perpendicular to the mirror line.