Non-Right-Angled Triangles (Edexcel IAL Maths)

Spec point — 3.1

Non-right-angled triangles

What is the sine rule, cosine rule and area rule for non-right-angled triangles?

• The Sine Rule, Cosine Rule and Area Formula can be used for ANY type of triangle
• They can help us calculate missing side lengths, angles and area

How do I know which rule to use?

• Once you know which rule to use, simply label your triangle, substitute in the values and rearrange if necessary

Exam Hint

• If you are given two angles in a triangle, finding the missing angle by subtracting from 180° might help.

• Make sure you are careful to pick the correct rule to use, you’ll need to remember all the rules as they aren’t in the formula booklet.

• Make sure your calculator is in degree mode (D).

• Always check your answers are sensible…

  • Have I remembered to square root at the end?
  • Have I remembered to use ^-1?

• Check if the question asks you to round your answer.

Worked Example