Year 8 - Maths
Using the sum of the interior angles of a triangle
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 use the fact that the interior angles of any triangle sum to 180° to find the size of missing angles.
Key Notes
- Missing angles in triangles can be found using the angle sum.
- Missing angles in triangles can be found using the angle sum and other triangle properties.
Vocabulary To Learn
- Interior angle: an angle formed inside a polygon by two of its edges.
- Sum: the total when numbers are added together.
Common Mistakes To Avoid
- Assuming triangles are certain types because of how they look.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
Missing angles in triangles can be found using the angle sum. Missing angles in triangles can be found using the angle sum and other triangle properties.
2. Use this key word in a maths sentence and explain it clearly. 'Interior angle'
an angle formed inside a polygon by two of its edges. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Assuming triangles are certain types because of how they look. Correction: Unless there is notation or it has stated the type of triangle you cannot assume.
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
- Interior angles of a polygon 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
Browse all guides in the Year 8 Maths guide library.