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GCSE Pythagoras revision

Use this Pythagoras revision page before testing your own triangle question in the solver tool.

Quick explanation

What this topic means and what to look for first.

Pythagoras is a core GCSE geometry topic built around right-angled triangles.

The main check is always whether the triangle is right-angled and whether you identified the hypotenuse correctly.

Step-by-step method

One reliable route through the topic.

  1. 1Confirm the triangle is right-angled.
  2. 2Identify the hypotenuse.
  3. 3Use a^2 + b^2 = c^2.
  4. 4Rearrange if you need a shorter side.
  5. 5Square root carefully and check the triangle length is sensible.
Worked examples

See the method in action.

Example 1

Find the hypotenuse when the other sides are 6 and 8.

  1. Use 6^2 + 8^2 = c^2.
  2. This gives 36 + 64 = 100.
  3. So c = 10.
Example 2

Find the missing shorter side when c = 10 and one side is 6.

  1. Use a^2 + 6^2 = 10^2.
  2. So a^2 + 36 = 100.
  3. Therefore a^2 = 64 and a = 8.
Common potential mistakes

Things that commonly send the method off track.

  • Using the longest side in the wrong place.
  • Applying Pythagoras when the triangle is not right-angled.
Follow-up access

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Follow-up access

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A free account is the current follow-up route for returning to the solver beta and future guide updates as the public library grows.

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FAQ

Short answers worth checking.

How do I know which side is the hypotenuse?

It is the longest side and it sits opposite the right angle.

Can Pythagoras give decimal answers?

Yes. Many valid side lengths are not whole numbers.

Related guides

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Next places to browse

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