Year 8 - Maths
Missing angles
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 solve problems that require a combination of angles facts to identify values of missing angles, providing explanations of reasoning and logic used.
Key Notes
- Missing angles can be found using parallel lines.
- Missing angles can be found using facts about triangles.
- Missing angles can be found in polygons using knowledge of exterior and interior angles.
- The relationship between interior and exterior angles can be used to find missing angles.
- Missing angles can be found by using a combination of all known facts.
Vocabulary To Learn
- Corresponding angles: A pair of angles at different vertices on the same side of a transversal in equivalent positions.
- Alternate angles: A pair of angles both between or both outside two line segments that are on opposite sides of the transversal that cuts them.
- Co-interior angles: Co-interior angles are on the same side of the transversal line and in between the two other lines.
- Interior angles: An interior angle is an angle formed inside a polygon by two of its edges.
- Exterior angle: An exterior angle is an angle on the outside of a polygon between an extension of an edge and its adjacent edge.
Common Mistakes To Avoid
- Pupils may work out missing angles without writing out their justifications.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
Missing angles can be found using parallel lines. Missing angles can be found using facts about triangles.
2. Use this key word in a maths sentence and explain it clearly. 'Corresponding angles'
A pair of angles at different vertices on the same side of a transversal in equivalent positions. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Pupils may work out missing angles without writing out their justifications. Correction: Each time a number which is not on the original diagram is used or found, an explanation should be given for where it has come from.
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
- 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.