Polygons
Polygons is a Grade 8 geometry skill in Saxon Math Course 3, Chapter 2, where students identify and classify polygons by number of sides and interior angles. Understanding polygon properties is essential for perimeter, area, geometric proofs, and real-world shape recognition.
Key Concepts
Property Polygons are closed plane figures with straight sides. They have the same number of sides as angles. A polygon is regular if all its sides are the same length and all its angles are the same size.
Examples A triangle is a polygon, but a circle is not because it has a curved side. A stop sign is a regular octagon because it has 8 equal sides and 8 equal angles. A rectangle is a polygon, but it's only regular if it's also a square.
Explanation Think of a polygon as a completely fenced in yard made only with straight fence pieces. If all the fence pieces are the same length and all the corners have the same angle, you’ve got a fancy 'regular' polygon! No curves or open gates are allowed in this exclusive geometry club.
Common Questions
What is a polygon?
A polygon is a closed 2D figure made of three or more straight sides. Examples include triangles, quadrilaterals, pentagons, and hexagons.
How are polygons classified?
Polygons are classified by number of sides: triangle (3), quadrilateral (4), pentagon (5), hexagon (6), and so on. They can also be regular (all sides and angles equal) or irregular.
What is the formula for the sum of interior angles of a polygon?
The sum of interior angles of a polygon with n sides is (n minus 2) times 180 degrees.
What is the difference between a convex and concave polygon?
A convex polygon has all interior angles less than 180 degrees. A concave polygon has at least one interior angle greater than 180 degrees.
Where are polygons taught in Grade 8?
Polygons are covered in Saxon Math Course 3, Chapter 2: Number and Operations and Geometry.