Lesson Plan

# Polygons

An introduction to some basic geometric figures and their place in the real world
Objectives

Students will be able to...

• define “polygon”
• classify the types of polygons
• differentiate polygons by the number of sides and angles (3-10)
Subjects
Math

#### 1 Hook

Activity: Exploring

Choose ten volunteers. With a ball of yarn, ask three students to pass the yarn between them to make a shape (students act as points/vertices). Note how students have modeled a closed shape that has three sides/edges. Students may recognize that the shape is a triangle. Continue adding one student, one point/side, and asking students what they observe. At this point, just acknowledge all student responses to assess what prior knowledge surfaces.

#### 2 Direct Instruction

Use BrainPOP’s “Polygons video to begin outlining today’s discussion. Next, define the characteristics of a “polygon”:

Polygon

• Has at least 3 sides (known as line segments or edges) and angles
• Is a closed plane (2D) figure
• Has straight line segments (no curves!)

Draw three basic polygons as examples (a triangle and two quadrilaterals) and three non-polygons (circle, key shape, heart). Ask student to vote as to whether each shape fulfills the criteria outlined in the definition of a polygon. Begin categorizing the polygon examples you drew by number of sides, and continue: trigon/triangle, tetragon/quadrilateral, pentagon, hexagon, heptagon/septagon, octagon, enneagon/nonagon, decagon. Where possible, highlight examples of each type of polygon found in the real world (triangle = pizza slice, pentagon = home plate, octagon = stop sign). Introduce new math terminology by discussing how polygons are classified: regular v. irregular, simple v. complex (self-intersecting), convex v. concave.

(Other related vocabulary: vertex/vertices, edge, line segment, angle, equilateral, equiangular)

#### 3 Guided Practice

Provide students with a 4-column graphic organizer that has the number of sides (3-10) already filled in (*see example below). Tackle each type of polygon one by one. For instance, instruct students to fill in “triangle” for a 3-sided polygon. Then give students ample time to explore forming triangles with Math Playground’s geoboard (found under math manipulatives). Use this opportunity to illustrate the new math terms: regular v. irregular, simple v. complex, convex v. concave. If possible, have students show their creations to each other, and point out the various shaped and sized triangles. Encourage students to define what they have created by using the new vocabulary (e.g., I created an irregular pentagon that is concave. I created a complex polygon that is a pentagon!) Lastly, have student draw examples, in this case a regular and irregular triangle.

 number of sides & angles name example of regular polygon example of irregular polygon 3 triangle (draw an example) (draw an example) 4

#### 4 Independent Practice

Using Explain Everything, have students create a presentation about each of the eight polygon types (trigon - decagon). If time is an issue, assign a different polygon to each student.

Each slide should include:

1. a diagram (hand drawn or image)

2. a label

3. working definition (number of sides)

4. an audio explanation (a.k.a., students “teach” each polygon type)

For an added bonus, they can add/draw an image that represents a real-world example of the polygon (e.g., pizza slice is a trigon/triangle; stop sign is an octagon).

#### 5 Wrap-Up

Challenge small groups of students to create their ideal dream house using regular polygons (of any size) on level one of Spaghetti Marshmallows (ignore the goal of placing a marshmallow in the circle). Encourage turrets, wings, garages, and various adornments. Ask students to screenshot final creation. If time permits, print out and have students label the polygons used in the architecture.