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The Cosine Rule
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Included angle and opposite side

Included angle and opposite side

Triangle labeled A, B and C with sides a, b and c, angle C highlighted as the included angle and side c shown opposite

The Cosine Rule works in any triangle, not only right-angled triangles. It is most useful when you know two sides and the included angle, or all three sides and want an angle.

The Cosine Rule Lesson

  1. IGCSE
  2. /Maths
  3. /The Cosine Rule

Step-by-step lessons on Edexcel IGCSE Maths The Cosine Rule. Each one builds up to exam-style questions. Build confidence with the shared Foundation-tier content first, since roughly 40% of Higher-tier marks are targeted at the grades 4–5 boundary that both tiers have in common.

Lessons