This line cuts the square into two equal parts, each of which is the mirror image of the other. This familiar example is called line symmetry.

Project the Symmetry Machine SketchPad file and ask the students to observe and describe what happens when you move a few squares. Have volunteers choose a square and predict what will happen when ...

After it rotates 90 degrees (one quarter turn), it looks the same as before. It is this transformation of an object so that the result is indistinguishable from the original that defines a symmetry.

Almost perfect What is particularly astonishing about the Red Square, the researchers say, is the degree of symmetry seen in lines, or "rungs," that bisect its surface.

This Maths article shows how the mirror line can help you to recognise vertical lines of symmetry on shapes and letters.

Peg uses a magic ukulele to find the line of symmetry on shapes.

Working with the remaining sketches These sketches portray a different type of line symmetry – vertical, horizontal, and oblique – with squares showing on only one side of the line of symmetry. The ...