8. Create lines of symmetry (FP)

teaches Common Core State Standards CCSS.Math.Content.4.G.A.3 http://corestandards.org/Math/Content/4/G/A/3
teaches Common Core State Standards CCSS.Math.Practice.MP2 http://corestandards.org/Math/Practice/MP2

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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)
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