What is a line of symmetry?
A line of symmetry (or mirror line) splits a shape into two halves that match exactly. If you folded the shape along the line, the two halves would fit perfectly on top of each other.
How many lines of symmetry?
| Shape | Lines of symmetry |
|---|---|
| Square | 4 |
| Rectangle | 2 |
| Equilateral triangle | 3 |
| Isosceles triangle | 1 |
| Scalene triangle | 0 |
| Rhombus | 2 |
| Kite | 1 |
| Parallelogram | 0 |
| Regular pentagon | 5 |
| Regular hexagon | 6 |
| Circle | endless (every line through the middle) |
Memory hook: a regular shape has as many lines of symmetry as it has sides.
Completing a reflection
To reflect a shape in a mirror line, each square goes the same distance from the line, on the other side.
- Pick a shaded square. Count how many squares it is from the mirror line.
- Count the same number of squares on the other side, and shade that square.
- Repeat for every square. The shape will look “flipped”.
Watch out! A rectangle’s diagonals are not lines of symmetry. Fold one corner to corner and the halves don’t match. And a parallelogram has none at all.
Top tip: trace the shape and fold the paper, or hold a mirror on the line to check.
👆 Letter mirror
Tap every letter with an up-and-down (vertical) line of symmetry
🪞 Complete the reflection1 of 3
Shade squares on the right to reflect the shape in the red mirror line.
🎮 Count the linesQuestion 1 of 5