Lesson objective: Divide two-dimensional figures in half using a line of symmetry.

This lesson helps to build fluency with finding lines of symmetry in two-dimensional fugures. Mirrors are used here because it highlights that a line of symmetry creates mirror images. This work develops students' understanding that a ine of symmetry is a line that divides a figure into two congruent figures that are mirror images of each other.

Students engage in Mathematical Practice 2 (reason abstractly and quantitatively) as they determine whether a figure is divided equally in two parts. Mirrors are used to help students visualize how a line of symmetry creates a mirror image.

**Key vocabulary:**

- equal
- line of symmetry
- symmetrical
- symmetry

**Special materials needed:**

- mirror (optional)