to build on students' knowledge of line symmetry and develop students' reasoning with properties of symmetry to develop an understanding of reflectional symmetry (e.g., what you do on one side, you do ...

That’s why a line of symmetry is sometimes called the mirror line. Sometimes you can fold a shape in half, and if it fits into itself perfectly with no overlaps you have found a line of symmetry.

Ultimately, in determining a symmetry of the square, there are really only two things to decide: where A goes (four choices) and where B goes (two choices). That means there are only 4 × 2 = 8 ...