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Lesson Title: Classification of Polygons

Class Level: VIII

Learning Objectives:

1. Students will be able to identify Polygon and Non-Polygon2. Students will be able to identify polygons as either Concave Polygon or Convex Polygon.3. Students will be able to name the polygons based on number of sides.

Material Required:

1. Charts2. Handout Papers3. Geoboards & Rubber bands4. Glue5. Magnet

Steps of Lesson

Explore: (10 mins)

1. Student Activity1. Draw a Triangle and a Circle. (chart 1)2. What is the difference in the shape of Triangle and Circle? (Let it describe by random

student)2. Knowledge to impart: Definition of Polygon: (write on board or on chart 2)

A polygon is any closed, 2-dimensional figure that is made up of only line segments.

Polygons can have any number of sides and angles, but the sides can never be curved.

The segments are called the sides of the polygons, and the points where the segments joined are called vertices. (vertex for one point) (chart 3)

Experience: (20 mins)

1. Student Activity:a. Distribute geo-boards and rubber bandsb. Make any shape using rubber bands on the geo-boards.c. Ask students, what type of shape they have formed. (Using Think-Pair-Share)

(Note: In Think-Pair-Share, students first think about the problem, pair with another student to orally clarify their ideas, then share their responses orally and/or in writing.)

d. Ask, whether the shape formed is polygon as defined?e. Ask, how many line segments made up that polygon?

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f. Ask several students to share their ideas with the whole class.

2. Knowledge to impart: Names of Polygons: (chart 4) Polygon is always named by the number of sides.

Name # of Sides Examples

Triangle 3

Quadrilateral 4

Pentagon 5

Hexagon 6

Heptagon 7

Octagon 8

Nonagon 9

Decagon 10

Ask, few students to tell the name of the polygon they got on the geoboard.

3. Knowledge to impart: (chart 5)a. Classification of Polygons as either Convex or Concave

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b. Polygons can be either convex or concave. The term concave refers to a cave, or the polygon is “caving in”. All stars are concave polygons.

A convex polygon does not cave in. Convex polygons look like:

c. Student Activity: i. Ask to identify the polygon just formed on the geoboard by the students as

either Convex Polygon or Concave Polygon.ii. Draw the shape on the given paper.

iii. Write T – table and put up the paper on the board under correct category.

Convex Polygon Concave Polygon

4. Knowledge to impart: (chart 5)a. A diagonal is a non-side line segment that connects two vertices of a polygon.

This pentagon has 5 diagonals.

b. Student Activity:

Explore the relationship between the number of sides of a convex polygon and its diagonals by completing the table.

Polygon Name Number of Sides Number of Diagonals

Example

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Triangle 3Quadrilateral 4Pentagon 5Hexagon 6Heptagon 7Octagon 8Nonagon 9Decagon 10

Draw one concave and one convex polygon and draw its diagonals. Observe that Polygons that are convex have no portions of their diagonals in their

exteriors.

Assessment: Polygon Quiz ( In pairs) (10 mins) The teacher will observe how the students organize their approach to the task

and evaluate their own processes. While walking around the room, the teacher will also ask questions that help

students think through the problem, think about alternative strategies, and reflect on their own thinking.

The teacher will analyze the students’ work and responses. Written assessment will be given that requires students to correctly categorize

Polygon and Non-Polygon, Convex and Concave Polygons by their properties and Naming the Polygons based on number of sides.

On the assessment, the students will be given an illustration that contains pictures of two-dimensional geometric shapes, including Convex and Concave Polygons, regular polygons, irregular polygons and non-polygons.

The assessment requires the student to analyze the shapes, compare and contrast properties, and categorize the shapes into appropriate categories.

Expand:

Collect pictures or objects of real life where different polygon shapes are used.

(example: Bee hive is in hexagonal shape)

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ASSESSESMENT

Name__________________Roll No.________Name________________Roll No.______

Polygon Quiz

Use the figures below to answer questions 1-6 on the following page.

A B C D

E F G H

I J K L

M N O

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Using the figures on the previous page, write the correct list of letters for each of the questions 1-6.

1. Which figures are not polygons? (Ans: )

2. Which figures are concave polygons? (Ans: )

3. Which figures are triangles? (Ans: )

4. Which figures are quadrilaterals? (Ans: )

5. Which figures are hexagons? (Ans: )

6. Which figures are octagons? (Ans: )

7. How many diagonals does a pentagon have? (Ans: )

8. The number of vertices a polygon has is always equal to the number of sides.

True, or false? (Ans: )

9. A convex polygon has one or more diagonals that go outside the polygon.

True, or false? (Ans: )

10. How many diagonals can be drawn in hexagon? (Ans: )

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A B C D E F G H

I J K L M N O

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Polygon Quiz:

Use the figures below to answer questions 1-6 on the following page.

A B C D

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E F G H

I J K L

M N O

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Using the figures on the previous page, write the correct list of letters for each of the questions 1-6.

1. Which figures are not polygons?

2. Which figures are concave polygons?

3. Which figures are triangles?

4. Which figures are quadrilaterals?

5. Which figures are hexagons?

6. Which figures are octagons?

7. How many diagonals does a pentagon have?

8. The number of vertices a polygon has is always equal to the number of sides. True, or false?

9. A convex polygon has one or more diagonals that go outside the polygon. True, or false?

10. An n-gon has n sides. A second polygon has twice as many sides. How many sides does the second polygon have?

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Expand:

1. Classification of Polygons as either Regular or Irregular.a. Student Activity:

i. Draw a quadrilateral. Check whether all the sides are equal in length.ii. Draw a quadrilateral whose sides are equal in length.

b. Definition: (Write on the board or on chart)i. A regular polygon is both Equiangular (all the angles are equal) and Equilateral

(all the sides are equal).

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