Lesson 19 Polygons Kalyani David

Objective 1. Define polygon 2. Identify and describe polygons by the number of sides and angles 3. Explain the difference between regular and irregular polygons

What is a Polygon???? Any ideas? Write down what you think it is for

A polygon is… a closed figure with three or more sides.

A polygon is a closed figure with 3 or more sides (all straight lines, no curves).

Check your work Polygon Not a polygon Not a polygon polygon polygon

Check your work Polygon polygon polygon Not a polygon Not a polygon

Where do we see Polygons in our everyday Environment ? Essential Question Where do we see Polygons in our everyday Environment ?

Classifying Polygons

A triangle has three sides. 1 3 2

A Quadrilateral has four sides. 4 3 1 2

A pentagon has five sides. 1 5 2 4 3

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

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

Key Question: 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. 1 2

Practice set and Written Practice from your Text Page:123 Home Work Practice set and Written Practice from your Text Page:123