Year 8 - Maths
Co-interior angles
Geometrical properties: polygons
Study Hub
Study Guides
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 recognise that a pair of parallel lines traversed by a straight line produces supplementary co-interior angles.
Key Notes
- Co-interior angles can be identified in an arrangement of 3 line segments.
- If two of the lines are parallel then these angles are supplementary.
- Knowledge of co-interior angles can be used to find unknown angles.
- Knowledge of co-interior, corresponding and alternate angles can be used to find unknown angles.
Vocabulary To Learn
- Co-interior: Co-interior angles are on the same side of the transversal line and in between the two other lines.
Common Mistakes To Avoid
- Pupils may believe that the co-interior angles are equal, like alternate and corresponding angles.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
Co-interior angles can be identified in an arrangement of 3 line segments. If two of the lines are parallel then these angles are supplementary.
2. Use this key word in a maths sentence and explain it clearly. 'Co-interior'
Co-interior angles are on the same side of the transversal line and in between the two other lines. 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 believe that the co-interior angles are equal, like alternate and corresponding angles. Correction: Have pupils draw a pair of parallel lines and a transversal line themselves, identify the co-interior angles, are they equal?
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
- 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
- Using the sum of the interior angles of a triangle Study Guide
Browse all guides in the Year 8 Maths guide library.