Determining which side
I can identify which side length is missing and use the appropriate form of Pythagoras' theorem to calculate it.
Determining which side
I can identify which side length is missing and use the appropriate form of Pythagoras' theorem to calculate it.
These resources will be removed by end of Summer Term 2025.
Lesson details
Key learning points
- The hypotenuse is the side opposite the right angle.
- It does not matter which of the shorter sides is identified as a or b.
Keywords
Right-angled triangle - A right-angled triangle has exactly one 90° interior angle.
Hypotenuse - A hypotenuse is the side of the right-angle triangle which is opposite the right-angle.
Pythagoras’ theorem - Pythagoras’ theorem shows that the sum of the squares of the two shorter sides of a right-angled triangle is equal to the square of its longest side (the hypotenuse).
Common misconception
I can only use Pythagoras' theorem to find the length of a side of a right-angled triangle when the right-angle marker is labelled, so I know which side is the hypotenuse.
The right-angle marker doesn't need to be explicitly labelled in order to be able to identify the right-angle. You can use knowledge of "interior angles in a triangle sum to 180°" to find the right angle, given two other angles.
To help you plan your year 9 maths lesson on: Determining which side, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your year 9 maths lesson on: Determining which side, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
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The assessment exit quiz will test your pupils' understanding of the key learning points.
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Explore more key stage 3 maths lessons from the Geometrical properties: similarity and Pythagoras' theorem unit, dive into the full secondary maths curriculum, or learn more about lesson planning.
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Starter quiz
6 Questions




Exit quiz
6 Questions



