MA30-06 Maths Coming soon
Trigonometric ratios of obtuse angles (Higher)
MA30-06
This lesson is coming soon.
In this lesson
Find the sine, cosine and tangent of an obtuse angle (90 to 180 degrees), including recognising that cosine is negative for an obtuse angle while sine stays positive.
What it covers
- Extend sin, cos and tan beyond 90 degrees, without requiring a right-angled triangle to contain the angle
- Know that sin(180-x) = sin(x): an obtuse angle has the same sine as its acute supplement
- Know that cos(180-x) = -cos(x): cosine changes sign for an obtuse angle
- Use a calculator correctly to evaluate sin/cos/tan of an obtuse angle directly
Key words
For: Edexcel IGCSE 4MA1
On the specification
| Board | Spec | Statement |
|---|---|---|
| Edexcel IGCSE 4MA1 | H4.8A | Understand and use sine, cosine and tangent of obtuse angles |
For teachers
This GCSE Maths lesson teaches trigonometric ratios of obtuse angles (Higher). By the end, students should be able to find the sine, cosine and tangent of an obtuse angle (90 to 180 degrees), including recognising that cosine is negative for an obtuse angle while sine stays positive. It works through two worked examples and the mistakes examiners report.