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Lesson 21 — Activity 2: Sorting Regular Polygons
Lesson 21 — Activity 2: Sorting Regular Polygons
Getting Ready
A polygon is a closed figure consisting of three or more straight sides. In this activity you will look at different polygons and classify them by either the number of sides or the lines of symmetry.
There are many different polygons. Look at this table to see polygons from 3 sides (a triangle) to 10 sides (a decagon). For this activity, you only need to remember the names of the three to six sided polygons.
It is important that you remember the names of the polygons up to six sides.

three sides — triangle

four sides — quadrilateral

five sides — pentagon

six sides — hexagon
Symmetry also exists outside of quadrilaterals.
Look at these regular polygons and see how many lines of symmetry they have.
An equilateral triangle has three internal angles and three lines of symmetry.
A regular pentagon has five internal angles and five lines of symmetry.
A regular hexagon has six internal angles and six lines of symmetry.
A regular octagon has eight internal angles and eight lines of symmetry.
Look at the number of sides and the number of lines of symmetry.
Do you see a pattern? In regular polygons, the number of sides equals the number of lines of symmetry.
Look at the number of sides and the number of lines of symmetry.
Do you see a pattern? In regular polygons, the number of sides equals the number of lines of symmetry.
Do you see a pattern? In regular polygons, the number of sides equals the number of lines of symmetry.