AI generatedGeometry and measuresGCSE Higher

Cosine rule - finding a side

Cosine rule: finding a side.

  • 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 side a. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Two sides and the included angle require the cosine rule.Substitute carefully, including the subtraction.Take the positive square root.
CalculatorKeep full accuracy, then round the final result.

Example 2

Find side a. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Two sides and the included angle require the cosine rule.Substitute carefully, including the subtraction.Take the positive square root.
CalculatorKeep full accuracy, then round the final result.

Your turn

Question 1

Find side a. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Check answer
Two sides and the included angle require the cosine rule.Substitute carefully, including the subtraction.Take the positive square root.
CalculatorKeep full accuracy, then round the final result.
Question 2

Find side a. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Check answer
Two sides and the included angle require the cosine rule.Substitute carefully, including the subtraction.Take the positive square root.
CalculatorKeep full accuracy, then round the final result.
Question 3

Find side a. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Check answer
Two sides and the included angle require the cosine rule.Substitute carefully, including the subtraction.Take the positive square root.
CalculatorKeep full accuracy, then round the final result.
Question 4

Find side a. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Check answer
Two sides and the included angle require the cosine rule.Substitute carefully, including the subtraction.Take the positive square root.
CalculatorKeep full accuracy, then round the final result.
Question 5

Find side a. Give your answer to 1 decimal place.

Triangle ABC; lengths in cmABCDiagram not to scale
Check answer
Two sides and the included angle require the cosine rule.Substitute carefully, including the subtraction.Take the positive square root.
CalculatorKeep full accuracy, then round the final result.
← All Geometry and measures cardsReport a mistake