Trigonometry
Right-angled triangles, then the sine and cosine rules for everything else, plus bearings and 3-D.
What this lesson covers
Trigonometry is a 8-part O Level Mathematics lesson. Each part makes one point and then hands over to the next, so it can be read in a sitting or picked up again at the part you stopped on. It defines the idea in plain words before using it, works through an example step by step, breaks the topic into its parts and compares them, shows where it is used outside the textbook, names the mistakes that cost marks in an exam, ends with a recap of what to remember.
How it begins
Trigonometry has two halves in this syllabus. Right-angled triangles use Pythagoras and the three ratios, sin, cos, tan. Any other triangle uses the sine rule, the cosine rule, and the area formula ½ab sin C. The first decision in every question is which toolkit applies, and it is decided by one thing: is there a right angle? The paper gives the sine rule, cosine rule and area formula.
The 8 parts
- Two toolkits
- Label from the angle, then choose the ratio
- Non-right triangles: sine rule or cosine rule?
- Angles beyond 90°
- Three dimensions
- Where marks go
- What to remember
- Watch one worked through
Practise Trigonometry
Everything on QuizByt for O Level Mathematics that goes with this lesson: read it first, then test yourself while it is fresh.
🧠 5 quizzes on Trigonometry (2 easy, 2 medium, 1 hard)
Work up from easy to hard: the hard quiz asks the O Level exam-style questions on Trigonometry.
🖨️ Printable worksheet
Trigonometry on paper for O Level, with room to write the working out. Preview the first page free.
🎮 Games for O Level Mathematics
Number and logic games at the right level for O Level. Passing a quiz on Trigonometry earns the credits that open them.
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