Year 9 - Maths
Choosing an appropriate method for finding lengths of a triangle
Trigonometry
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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 learn how to recognise the relationship between the unit circle and the trigonometric ratios of sine, cosine and tangent. Pupils then apply this knowledge to solve trigonometric problems.
Lesson Summary
You will learn to choose the appropriate method to find the missing side in a right-angled triangle.
Key Notes
- Trigonometry can be useful in many practical situations.
- You can use it to find the height of objects.
- You can use it to find the length of an object given the length of its shadow.
- Sometimes it may be better to use Pythagoras' theorem.
Vocabulary To Learn
- Trigonometric ratios: The trigonometric ratios are ratios between each pair of lengths in a right-angled triangle.
Common Mistakes To Avoid
- Pupils may struggle to find a right-angled triangle within the context of the question.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
Trigonometry can be useful in many practical situations. You can use it to find the height of objects.
2. Use this key word in a maths sentence and explain it clearly. 'Trigonometric ratios'
The trigonometric ratios are ratios between each pair of lengths in a right-angled triangle. 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 struggle to find a right-angled triangle within the context of the question. Correction: Encourage the pupils to sketch the question and consider adding a perpendicular line to the diagram.
More Lessons In This Unit
- Checking and securing understanding of Pythagoras' theorem Study Guide
- Checking and securing understanding of similar triangles Study Guide
- Choosing the right trigonometric ratio Study Guide
- Problem solving with trigonometry Study Guide
- Scaling the right-angled triangle from the unit circle Study Guide
- Sine and cosine ratios Study Guide
- Tangent ratio Study Guide
- The unit circle Study Guide
- Using the cosine ratio Study Guide
- Using the sine ratio Study Guide
- Using the tangent ratio Study Guide
Browse all guides in the Year 9 Maths guide library.