Line of Symmetry and Reflection Symmetry

A rectangle has two lines of symmetry. One runs vertically down the middle and one runs horizontally across the middle. Fold the rectangle along either line and the two halves match exactly. Because it has at least one line of symmetry, a rectangle also has reflection symmetry.

A square has four lines of symmetry, including two diagonal lines from corner to corner. The other two pass through the middle of each pair of opposite sides. Every line splits the square into two matching halves, which gives the square reflection symmetry.

A circle has infinitely many lines of symmetry. Every line that passes through its centre splits the circle into two matching halves, so no other shape has more. Because it has at least one line of symmetry, a circle also has reflection symmetry.

The number depends on the type of triangle. An isosceles triangle has one line of symmetry, while an equilateral triangle has three. Folding the triangle along any of these lines produces two matching halves, so both types of triangle have reflection symmetry.

A line of symmetry is the actual line that divides a shape into two matching, mirror-image halves. Reflection symmetry is the property a shape has when it contains at least one line of symmetry. In short, the line is the feature, and reflection symmetry is what we call having it.

To find a line of symmetry, draw a line across the shape, then check whether the two halves are identical. If folding along the line makes both halves match exactly, it is a line of symmetry. Test lines in different directions, as a shape can have more than one.