The document discusses how two sides of a shape fit exactly into each other, making the dotted line down the middle a line of symmetry. It also notes that a rectangle can be rotated 180 degrees to fit onto itself twice, giving it an order of rotational symmetry of 2.

1. The two sides fit
into each other
exactly. So the
dotted line is called
the line of
symmetry

2. The two rectangle fitted
on itself two times. So
the order of rotational
symmetry is 2.