--- title: "Regular and irregular polygons" description: "Distinguish between regular and irregular polygons based on reasoning about equal sides and equal angles" canonical: https://lightmysky.com/learn/mathematics/regular-and-irregular-polygons-mt_8H2kO4k2B9 source: https://lightmysky.com/learn/mathematics/regular-and-irregular-polygons-mt_8H2kO4k2B9.md retrieved: 2026-10-19 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Regular and irregular polygons Distinguish between regular and irregular polygons based on reasoning about equal sides and equal angles Subject: Mathematics · Area: Geometry · Ages 9 to 10 Page: https://lightmysky.com/learn/mathematics/regular-and-irregular-polygons-mt_8H2kO4k2B9 ## Ready when they can - 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 ## Lesson: Regular and irregular polygons Look at a stop sign: its eight sides all match, and so do its eight corners. 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. *(drawing: This pentagon has 5 equal sides and 5 equal angles, so it is regular.)* **Example.** 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. The number of sides never decides it. A triangle with 3 matching sides and 3 matching angles is regular, and so is an octagon, a polygon with 8 sides, when all 8 sides and all 8 angles match. **Tip.** 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. **Recap.** Regular polygons have every side and every angle matching; if sides or angles differ, the polygon is irregular. ## Practice 18 questions on this page, each with its working shown. ## Needs first - [Classifying quadrilaterals](https://lightmysky.com/learn/mathematics/classifying-quadrilaterals-mt_Xt1cRqaBOW) - [Estimating Angles](https://lightmysky.com/learn/mathematics/estimating-angles-mt_YUJ5pwalqL) ## Opens up - [2-D shapes (age 10+)](https://lightmysky.com/learn/mathematics/2-d-shapes-age-10-mt_hdrMoiTgqu) - [Classifying shapes by properties](https://lightmysky.com/learn/mathematics/classifying-shapes-by-properties-mt_liIW336odh) - [Geometric terms and notation](https://lightmysky.com/learn/mathematics/geometric-terms-and-notation-mt_WtIFJSCQIT) - [Precise Maths Vocabulary](https://lightmysky.com/learn/mathematics/precise-maths-vocabulary-mt_xfwv0M83mJ)