Year 9 - Maths
Choosing the right trigonometric ratio
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 trigonometric ratio to use to solve problems in right-angled triangles.
Key Notes
- When selecting the appropriate trigonometric ratio, consider what information you have been given.
- When selecting the appropriate trigonometric ratio, consider what you are trying to find.
- If you do not have enough information, consider what you need and how you will get it.
- Trigonometric ratios involve two lengths and an angle.
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 believe the horizontal edge of the triangle is always the adjacent.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
When selecting the appropriate trigonometric ratio, consider what information you have been given. When selecting the appropriate trigonometric ratio, consider what you are trying to find.
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 believe the horizontal edge of the triangle is always the adjacent. Correction: Emphasise that the labelling of the triangle is based around the focus angle and use right-angled triangles with various orientations.
More Lessons In This Unit
- Checking and securing understanding of Pythagoras' theorem Study Guide
- Checking and securing understanding of similar triangles Study Guide
- Choosing an appropriate method for finding lengths of a triangle 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.