9.1 Polygons
In this topic, students learn about polygons, the relationship between the number of sides, vertices and diagonals, and how to draw, label and name polygons.
Learning Objectives
- State the relationship between the number of sides, vertices and diagonals of polygons.
- Determine the number of vertices and diagonals of a polygon.
- Draw polygons according to the number of sides.
- Label the vertices of polygons.
- Name polygons according to their number of sides.
Know Polygons
Learn the meaning of polygons, examples of shapes and polygon names according to the number of sides.
Brief Explanation
What is a Polygon?
Poligon is a closed shape on a plane bounded by three or more straight lines.
How is a polygon named?
A polygon is named according to the number of its sides. For example, a polygon with 6 sides is called a hexagon.
| Number of sides | Name of polygon | Brief note |
|---|---|---|
| 3 | Triangle | Polygon with 3 sides |
| 4 | Quadrilateral | Polygon with 4 sides |
| 5 | Pentagon | Polygon with 5 sides |
| 6 | Hexagon | Polygon with 6 sides |
| 7 | Heptagon | Polygon with 7 sides |
| 8 | Octagon | Polygon with 8 sides |
| 9 | Nonagon | Polygon with 9 sides |
| 10 | Decagon | Polygon with 10 sides |
Interactive: Explore Polygons
Choose a polygon name to see its number of sides, vertices, diagonals and angles.
Triangle
3-sided polygon.
Try Answering First
Read the question, answer it in your mind, then press “Check Answer”.
What is the meaning of polygon?
Name the polygon that has 8 sides.
Find the number of vertices for a polygon with 10 sides.
Common Mistakes
- Thinking that an open shape is a polygon. A polygon must be a closed shape.
- Using curved lines as polygon sides. Polygon sides must be straight lines.
- Naming polygons wrongly, for example, 6 sides is a hexagon, not a pentagon.
- Not labelling vertices in alphabetical order.
- Marking three or more points in a straight line when drawing a polygon.
Misconceptions
All closed shapes are polygons.
A polygon must have sides made of straight lines.
The name of a polygon depends on the size of the shape.
The name of a polygon depends on the number of sides.
Vertex labels can be placed randomly.
Vertices are usually labelled in alphabetical order.
Summary
- A polygon is a closed shape with three or more straight lines.
- The number of vertices of a polygon is the same as the number of its sides.
- The name of a polygon is determined by its number of sides.
- To draw a polygon, mark the points, join the points, label the vertices and name the polygon.
- The number of diagonals can be found using the given steps or the formula n(n − 3) / 2.
Short Activity
Complete all parts first, then press the check answer button.
A. Objective Quiz
1 A polygon is a on a plane with sides made of straight lines.
2 A polygon that has 6 sides is called a .
B. Fill in the Blanks
3 A polygon that has 3 sides is called a .
4 A polygon that has 5 sides is called a .
C. Drag and Drop: Arrange the Steps to Draw a Polygon
Drag each step to the correct place. On a phone, tap the answer choice first, then tap the sequence box.
