Symmetry

Isosceles triangle, Letter 'A', Kite shape

Isosceles triangle has one line through its vertex and base midpoint. Letter 'A' has one vertical line. Kite shape has one line through its axis. Rectangle has 2 lines, circle has infinite lines.

120°, 240°, 360°

If a figure has exactly 3 angles of rotational symmetry, the smallest angle is 360°÷3 = 120°. The angles are multiples of 120°: 1×120°=120°, 2×120°=240°, 3×120°=360°.

8

The order of rotational symmetry equals the number of sides for a regular polygon. A regular octagon has 8 sides, so its order of rotational symmetry is 8. It can be rotated 8 different ways and look the same.

They overlap exactly

When you fold a figure along its line of symmetry, the two halves overlap exactly - they are mirror images of each other. This is the defining property of a line of symmetry.