Line Symmetry
Grade 2What is a line of symmetry?
A line of symmetry divides a shape into two halves that are mirror images of each other. If you folded the shape along that line, the two halves would sit exactly on top of one another.
Not every shape has one. A scalene triangle has none. An equilateral triangle has three. A circle has infinitely many.
Lines of symmetry in common shapes
Square: 4 lines. Rectangle: 2 lines (horizontal and vertical only — the diagonals are not lines of symmetry). Regular hexagon: 6 lines. Isosceles triangle: 1 line. Kite: 1 line (the longer diagonal).
The diagonals of a rectangle are not lines of symmetry — folding along a diagonal gives a triangle, not the same shape. Diagonals of a square are lines of symmetry.
Using symmetry to find coordinates
EXAMPLE
Shape ABCD has a vertical line of symmetry at x = 3. Point A is at (1, 4). Find the coordinates of the mirror image of A.
Point A is 3 − 1 = 2 units to the left of the line x = 3. Its mirror is 2 units to the right: x = 3 + 2 = 5. The y-coordinate stays the same. Mirror of A = (5, 4).
