AI generatedGeometry and measuresGCSE Higher

Cosine rule - finding an angle

Cosine rule: finding an angle.

  • Label the sides and angles before choosing a rule.
  • Sine rule: matching opposite pairs. Cosine rule: three sides or two sides and the included angle.
  • Use degree mode. Keep full calculator accuracy until the final rounding step.

Example 1

Find angle A. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Use the cosine rule when all three sides are known.The side opposite A is a.Use inverse cosine.
CalculatorKeep full accuracy, then round the final result.

Example 2

Find angle A. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Use the cosine rule when all three sides are known.The side opposite A is a.Use inverse cosine.
CalculatorKeep full accuracy, then round the final result.

Your turn

Question 1

Find angle A. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Check answer
Use the cosine rule when all three sides are known.The side opposite A is a.Use inverse cosine.
CalculatorKeep full accuracy, then round the final result.
Question 2

Find angle A. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Check answer
Use the cosine rule when all three sides are known.The side opposite A is a.Use inverse cosine.
CalculatorKeep full accuracy, then round the final result.
Question 3

Find angle A. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Check answer
Use the cosine rule when all three sides are known.The side opposite A is a.Use inverse cosine.
CalculatorKeep full accuracy, then round the final result.
Question 4

Find angle A. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Check answer
Use the cosine rule when all three sides are known.The side opposite A is a.Use inverse cosine.
CalculatorKeep full accuracy, then round the final result.
Question 5

Find angle A. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Check answer
Use the cosine rule when all three sides are known.The side opposite A is a.Use inverse cosine.
CalculatorKeep full accuracy, then round the final result.
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