What is a Line of Symmetry?
Imagine you have a picture of a butterfly. If you fold the picture exactly in the middle, the left side fits perfectly over the right side. The line along which you fold the paper is called the Line of Symmetry (or Axis of Symmetry).
Tip
Definition: A line that cuts a figure into two parts that exactly overlap (coincide) when folded along that line is called a Line of Symmetry.
This is also known as Reflection Symmetry because one half acts like a mirror reflection of the other half.
Figures with One Line of Symmetry
Some shapes have only one way to be folded to overlap perfectly. An isosceles triangle (with only two equal sides) is a good example.
Figures with Multiple Lines of Symmetry
Some figures are very regular and can be folded in many ways.
- Rectangle: Has 2 lines of symmetry (vertical and horizontal). Note: The diagonal is NOT a line of symmetry for a non-square rectangle.
- Square: Has 4 lines of symmetry (vertical, horizontal, and two diagonals).
- Equilateral Triangle: Has 3 lines of symmetry.
Reflection Symmetry
When we look into a mirror, we see a reflection. If an object is placed before a mirror, the image formed is symmetrical to the object with respect to the mirror line.
- Left becomes Right.
- Right becomes Left.
This property is used in paper cutting. If you fold a paper and cut a shape, unfolding it reveals a symmetric pattern where the fold line is the line of symmetry.