Lesson 19 Polygons

Kalyani David

1. Define polygon2. Identify and describe polygons by the number of sides and angles3. Explain the difference between regular and irregular polygons

Objective

What is a Polygon????

Any ideas?

Write down what you think it is for

a closed figure with three or more sides.

A polygon is…

A polygon is a closed figure

with 3 or more sides

(all straight lines, no curves).

Check your work

Polygon Not a polygonNot a polygon polygon

Polygon Not a polygonpolygon

Not a polygon

Check your work

Polygon polygon polygon Not a polygon

Polygon Not a polygonNot a polygon Polygon

Essential Question

Where do we see Polygons in our everyday Environment ?

Classifying Polygons

Triangle A triangle has three sides.

1

2

3

Quadrilateral A Quadrilateral has four sides.

1

2

3

4

Pentagon A pentagon has five sides.

1

2

3

4

5

Hexagon

A hexagon has six sides.

Heptagon

A heptagon has seven sides.

heptagon

Octagon

An octagon has eight sides.

8 sided Polygon = Octagon

Hint: “oct”opus – 8 legs

Number of Sides Name

3 Triangle

4 Quadrilateral

5 Pentagon

6 Hexagon

7 Heptagon

8 Octagon

9 Nonagon

10 Decagon

11 Hendecagon

12 Dodecagon

Classifying Polygons by

number of Sides

Q: What do we call a polygon with more than 12 sides?

A : An ‘n’-gon where ‘n’ is the number of sides

Ex: a 20 sided polygon is a 20-gon

Let’s Review:

The triangle is the smallest polygon. It only has three sides.

A pentagon has five sides. A hexagon has six sides. A heptagon has seven sides. An octagon has eight sides.

Match these.

Triangle eight sides

Heptagon three sides

Octagon seven sides

Match some more.

Pentagon four sides

Hexagon five sides

Square six sides

A triangle is the smallest polygon because it has three sides. Can you have a two-sided polygon? Why or why not?

Two lines don’t close to make a shape. They make an angle.

2

1

Key Question:

Practice set and Written Practicefrom your Text

Page:123

Home Work