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When Sine Rule Fails
When Sine Rule Fails
Sometimes you know two sides and the angle BETWEEN them (SAS), or all three sides (SSS) but no angles. The sine rule can't help - it needs a matched pair! That's when you reach for the cosine rule.
Now try it yourself
Quiz · Question 1 of 12
Which formula is the cosine rule for finding side a?
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This topic in real past papers
Every real exam question we've found on cosine rule, with a full worked answer.
AQA Paper 3
Two of the four sittings we have full papers for require the sine rule or cosine rule to be used to find a missing angle in a triangle that is not right-angled.
Edexcel Paper 2
All three sittings we have full papers for test trigonometry to find a missing length or angle, and June 2019 tests it twice: once in a simple right-angled triangle and once inside a 3D solid.