Unit 8, Lesson 4
Symmetry in Figures (Part 1)
Grade 4
Preparation
Lesson Purpose
The purpose of this lesson is to introduce the concept of line symmetry and for students to identify lines of symmetry in two-dimensional figures.
Lesson Narrative
This lesson introduces students to symmetry as an attribute of two-dimensional figures. Students relate lines of symmetry to the lines of folding that create two identical halves: if a figure is folded along or mirrored across such a line, the two halves would overlap and match exactly. The idea of folding along or mirroring across a line is essential here, as there are some figures that could be decomposed into two identical halves but have no line symmetry.
After reasoning about the meaning of lines of symmetry from examples and non-examples, students work to identify figures that have line symmetry and draw lines of symmetry.
- Representation
- MLR8
- Comprehend (in spoken and written language) the meaning of the term “line of symmetry."
- Explain (orally and in writing) how to determine if a figure has 1 or more lines of symmetry.
- Let’s describe symmetry in flat figures.
Required Materials
Activity 3
Required Preparation
Activity 1
- Make copies of the set of figures in the second question available for cutting and for demonstration during the Lesson Synthesis.
Activity 2
- Sort the shape cards from the previous lessons into three groups of 12 cards (A–L, M–X, and Y–JJ).
Teacher Reflection Questions
What ideas do students have about symmetry? How will you leverage those ideas in the next lesson?
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