Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!
Print

Maths

Trigonometry - Higher

Finding the length of the opposite side

Question

Find the length of side BC.

image: 7cm traingle

toggle answer

Answer
  • We are given angle A and side AB.
  • AB is the hypotenuse.
  • BC is opposite angle A.
  • Therefore we use the formula:
  • sin = opposite / hypotenuse
  • sin 30 = BC / 7
  • Multiply both sides by 7
  • 7 x sin30 = BC
  • Using a calculator we get
  • BC = 3.5cm

Now you try this one.

Question

Find length of side PQ, giving your answer correct to 3 sf.

image: triangle

toggle answer

Answer

The answer is 4.77cm (3 sf).

  • Can you see that PQ is opposite the given angle and that QR is adjacent to it?
  • Use the formula:
  • tan = opposite / adjacent
  • tan50 = PQ / 4
  • 4 × tan50 = PQ
  • PQ = 4.77 (3 sf)

Back to Geometry and measures index

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.