1.4 Axis of symmetry An axis (line) of symmetry divides a fi gure into two mirror image halves.
By the end of this section you should:
● understand how to draw the axis of symmetry of a given shape
If you can refl ect (or fl ip) a fi gure over a line and the fi gure appears unchanged, then the fi gure has refl ection symmetry or an axis (line) of symmetry. The line that you refl ect through is called the axis of symmetry.
Some shapes have one line of symmetry, some shapes have many lines of symmetry and some shapes have no lines of symmetry.
Here are some examples. Rectangles
If you try to fold this rectangle along the dotted line, the two halves don’t match up.
Triangles
So this is not a line of symmetry.
If you fold it along the dotted line below, the folded parts sit perfectly together, with all edges matching.
Equilateral triangle All sides equal All angles equal 3 lines of symmetry