Polygons Part 2
Names of Polygons
You name a polygon by the number of sides it contains. Use the chart below.
| # of sides | Name |
| 3 | triangle |
| 4 | quadrilateral |
| 5 | pentagon |
| 6 | hexagon |
| 7 | heptagon |
| 8 | octagon |
| 9 | nonagon |
| 10 | decagon |
| 11 | hendecagon |
| 12 | dodecagon |
| n sides | n-gon |
n-gon
Notice the last row has "n" sides. This is primarily used for polygons when the number of sides are greater than 12.
Replace the "n" with the number of sides.
For instance, a polygon with 13 sides would be called a 13-gon.
What would a polygon with 46 sides be called?
Answer: 46-gon
Your Turn
Identify the polygons by name.
Answer: pentagon
Answer: decagon
Answer: heptagon
Answer: octagon
Answer: quadrilateral
Equilateral and Equiangular
We can also identify a polygon as:
equilateral - all sides congruent
equiangular - all angles are congruent
Regular Polygons
If a figure has all sides congruent and all angles congruent then it is called a regular polygon.
A square is a regular quadrilateral because all four sides are congruent and all four angles are right.
Classify Polygons
You can now:
- Classify a polygon as convex or concave
- Name the polygon by the number of sides
- Identify if the polygon is equilateral, equiangular or both - thus regular or neither
Try This One
Classify this polygon:
Concave or Convex
Answer: Concave
pentagon
hexagon
heptagon
octagon
Answer: hexagon
equilateral
equiangular
regular
neither
Answer: neither
Classify Polygons
Look at the figure and see if you can decide who is correct in classifying the polygon.
Chase said convex, regular, quadrilateral.
Anna said convex, equiangular, quadrilaterl.
Who is correct and why?
Answer: Anna; The sides are not congruent so it is not regular. Anna is correct.
