Year 11 - Maths
The cosine rule
Non right-angled trigonometry
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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 explore how to apply knowledge in trigonometry to non right-angled triangles.
Lesson Summary
You will learn to derive the formula for the cosine rule.
Key Notes
- There are multiple ways to prove the cosine rule
- When deriving (or proving) it is sometimes useful to derive other information
Vocabulary To Learn
- Cosine rule: The cosine rule is a formula used for calculating either an unknown side length or the size of an unknown angle.
Common Mistakes To Avoid
- Pupils may not see the need for this rule as they have the sine rule.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
There are multiple ways to prove the cosine rule. When deriving (or proving) it is sometimes useful to derive other information.
2. Use this key word in a maths sentence and explain it clearly. 'Cosine rule'
The cosine rule is a formula used for calculating either an unknown side length or the size of an unknown angle. 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 not see the need for this rule as they have the sine rule. Correction: The sine rule can be used in many cases but it is not always the most efficient. There will be problems where it will be much faster to use the cosine rule.
More Lessons In This Unit
- Calculating the area of any triangle when the height is not known Study Guide
- Checking and securing understanding of trigonometric ratios Study Guide
- Considering the appropriate trigonometric rule Study Guide
- Drawing the sine and cosine graphs Study Guide
- Drawing the tangent graph Study Guide
- Interpreting the trigonometric graphs Study Guide
- Problem solving with non right-angled trigonometry Study Guide
- The area of any triangle Study Guide
- The sine rule Study Guide
- Using the sine and cosine rules Study Guide
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