Regular and irregular polygons
Distinguish between regular and irregular polygons based on reasoning about equal sides and equal angles
What a learner can do afterwards
- Classify a set of polygons as regular or irregular
- Explain that a regular pentagon has 5 equal sides and 5 equal angles
- Identify that a rectangle is irregular (equal angles but not all equal sides) unless it is a square
The lesson
A polygon is a flat shape with straight sides. It is regular when every side is the same length and every angle is the same size. If even one side or angle is different, the polygon is irregular.
A square has 4 equal sides and 4 right angles, so it is regular. A rectangle also has 4 right angles, but two sides are longer than the other two, so most rectangles are irregular.
When you check a polygon, look at the sides first, then the angles. Both have to match for the shape to be regular. If either one is off, the polygon is irregular.
Regular polygons have every side and every angle matching; if sides or angles differ, the polygon is irregular.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.