Year 8 - Maths
Interior angles of a polygon
Geometrical properties: polygons
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
In this unit pupils will investigate internal and external angles of polygons and angles made with a transveral and parallel lines. Pupils will develop their ability to formally prove properties of polygons to generalise.
Lesson Summary
You will learn to find the interior angle of any polygon.
Key Notes
- Any polygon can be split into triangles.
- Using these triangles you can demonstrate the rule for the interior angle sum of a polygon.
- A missing interior angle in any polygon can be found.
Vocabulary To Learn
- Polygon: A polygon is a flat (2D), closed figure made up of straight line segments.
- Interior angle: An interior angle is an angle formed inside a polygon by two of its edges.
- Sum: The sum is the total when numbers are added together.
Common Mistakes To Avoid
- When splitting a polygon into triangles, pupils may draw line segments that cross inside the shape.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
Any polygon can be split into triangles. Using these triangles you can demonstrate the rule for the interior angle sum of a polygon.
2. Use this key word in a maths sentence and explain it clearly. 'Polygon'
A polygon is a flat (2D), closed figure made up of straight line segments. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: When splitting a polygon into triangles, pupils may draw line segments that cross inside the shape. Correction: By choosing a single common vertex for all the triangles, the line segments will not cross inside the shape.
More Lessons In This Unit
- Alternate angles Study Guide
- Angles on parallel lines traversed by a straight line Study Guide
- Checking understanding of angles from KS2 Study Guide
- Co-interior angles Study Guide
- Corresponding angles Study Guide
- Deriving the sum of interior angles in multiple ways Study Guide
- Exterior angles of polygons Study Guide
- Formal angle notation Study Guide
- Formalising understanding of triangles from KS2 Study Guide
- Interior and exterior angles of regular polygons Study Guide
- Missing angles Study Guide
- Problem solving with polygons Study Guide
- Securing understanding of angles from KS2 Study Guide
- The sum of the interior angles of any triangle Study Guide
- Using the sum of the interior angles of a triangle Study Guide
Browse all guides in the Year 8 Maths guide library.