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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 covering CIE IGCSE Maths The Cosine Rule for Core and Extended tier. Each lesson works through exam-style questions in Paper 1 and Paper 3 (Core) or Paper 2 and Paper 4 (Extended) format. Start with the Core-tier fundamentals in number and algebra before moving on to the more demanding Extended-only topics like calculus-adjacent algebra and advanced trigonometry.

Lessons

SurdsBoundsDirect and Inverse ProportionQuadratic FormulaFactorising Harder QuadraticsAlgebraic FractionsRearranging Harder FormulaeFinding the Area of Any TriangleThe Sine RuleThe Cosine Rule3d Pythagoras and TrigonometryThe Magnitude of a VectorHistogramsConditional Probability