Right-Angled Triangles (Edexcel IAL Maths)

Spec point — 3.1

Right-angled triangles

What is SOHCAHTOA?

• SOH, CAH, and TOA are an easy way to remember the three basic trigonometry ratios

• They show the relationship between an angle and the different sides of a right-angled triangle which we can label Hypotenuse, Adjacent and Opposite

• We use them to find missing angles and sides for right‑angled triangles

  • Hypotenuse is the longest side of a right-angled triangle
  • Adjacent is the side next to the angle you are working with (in between the angle and the right angle)
  • Opposite is the side opposite the angle you are working with

• We use the inverse trig functions to find missing angles

How do I use SOHCAHTOA?

Exam Hint

• Remember SOHCAHTOA are only for calculating missing sides and angles for right‑angled triangles

  • For non-right‑angled triangles you will need to use the Sine or Cosine rules.

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

• Always check your answers are sensible…

  • Should my answer be longer or shorter than the sides I have already i.e. is it the hypotenuse?
  • Is my angle sensible…
  • Have I remembered to use ^-1?

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

Worked Example