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Year 9
Pythagoras’ Theorem
Definition
Pythagoras’ theorem links the three sides of a right-angled triangle. The square of the hypotenuse equals the sum of the squares of the other two sides.
Why Do I Have to Learn This?
Pythagoras links the three sides of a right-angled triangle. Builders, sailors and game designers use it to find distances they cannot measure directly.
Key Rules:
- 1. The theorem works only for right-angled triangles.
- 2. The hypotenuse is the longest side, opposite the right angle.
- 3. a² + b² = c², where c is the hypotenuse.
Remember:
- •For sides 3 and 4, the hypotenuse is 5.
- •Square the sides, then add or subtract, before taking a root.
- •The hypotenuse is always the longest side.
Hypotenuse
The longest side of a right-angled triangle, opposite the right angle. By Pythagoras' theorem, hypotenuse² = a² + b².
If the two shorter sides are 3 and 4, the hypotenuse is 5, because 3² + 4² = 5².
Animated Example:
3² + 4² = 25, so c = 5
Free Pythagoras’ Theorem Worksheet
Download free worksheets and practise today.
Every download has a fresh set of questions.
Let’s Practise the Concept
Step 1 of 3
Put them in order
Tap the numbers from smallest to largest.
In order so far: nothing yet