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Non-Right-Angled Triangles (Edexcel International A Level Maths: Pure 1)
Revision Note
Non-Right-Angled Triangles
What do I do if there isn’t a right‑angle?
- The Sine Rule, Cosine Rule and Area Formula can be used for ANY type of triangle
- They can help us calculate missing side lengths, angles and area
How do I know which rule to use?
- Once you know which rule to use, simply label your triangle, substitute in the values and rearrange if necessary
Examiner Tip
- If you are given two angles in a triangle, finding the missing angle by subtracting from 180° might help.
- Make sure you are careful to pick the correct rule to use, you’ll need to remember all the rules as they aren’t in the formula booklet.
- Make sure your calculator is in degree mode (D).
- Always check your answers are sensible…
- Have I remembered to square root at the end?
- Have I remembered to use -1?
- Check if the question asks you to round your answer.
Worked example
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