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Lesson 13 of 18
  • Year 9

Further demonstrating of Pythagoras' theorem

I can appreciate there is a relationship between the lengths of the sides of a right-angled triangle.

Lesson 13 of 18
New
New
  • Year 9

Further demonstrating of Pythagoras' theorem

I can appreciate there is a relationship between the lengths of the sides of a right-angled triangle.

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Lesson details

Key learning points

  1. A visual approach can help you understand the structure behind Pythagoras' theorem.
  2. There is a difference between proof and demonstration.
  3. A demonstration would be showing Pythagoras' theorem works for specific right-angled triangles.
  4. A proof is generalised i.e. using four congruent triangles arranged in a particular way inside a square.
  5. The sum of the squares of the two shorter sides equals the square of the longest side.

Keywords

  • 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

Pythagoras' theorem is just a relationship between the three sides of a right-angled triangle.

Whilst this is true, Pythagoras' theorem can more visually be represented as three squares whose sides are equal in length to the three sides of the triangle. The sum of the areas of the two smaller squares is equal to the area of the larger square.


To help you plan your year 9 maths lesson on: Further demonstrating of Pythagoras' theorem, download all teaching resources for free and adapt to suit your pupils' needs...

When students are identifying whether the largest angle in a triangle they have constructed, the angle may be ambiguous. Advise them to use a protractor with caution, as accurate measuring of the angles may be tricky with several moving pieces.
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This content is © Oak National Academy Limited (2026), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Prior knowledge starter quiz

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6 Questions

Q1.
Which of these are square numbers?

Correct answer: 16
Correct answer: 1
3
8

Q2.
Match each statement to its value.

Correct Answer:7 squared,49

49

Correct Answer:the square of 8,64

64

Correct Answer:the square root of 9,3

3

Correct Answer:the square of 1,1

1

Correct Answer:root 16,4

4

Q3.
The difference between 10² and 6² is .

Correct Answer: 64

Q4.
9² + 6² – 4² = .

Correct Answer: 101

Q5.
Starting with the smallest, place these angles in order of size.

1 - zero degrees
2 - acute angle
3 - obtuse angle
4 - straight line angle
5 - reflex angle

Q6.
Which two of these are not square numbers?

64
Correct answer: 55
16
Correct answer: 12
81

Assessment exit quiz

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6 Questions

Q1.
What is the missing side length of a right-angled triangle with legs of size 3 and 4 units?

Correct Answer: 5, 5 units

Q2.
What is the missing side length of a right-angled triangle with legs of size 6 and 8 units?

Correct Answer: 10, 10 units

Q3.
What is the missing side length of a right-angled triangle with hypotenuse 13 units, and a shorter side of length 5 units?

Correct Answer: 12 units, 12

Q4.
What is the area of a right angled triangle with hypotenuse of length 25 units, and base of length 7 units?

Correct Answer: 84, 84 square units

Q5.
The lengths of sides of different triangles are provided below. Which ones are right angled triangles?

Correct answer: 3, 4, 5
Correct answer: 119, 120, 169
Correct answer: 44, 117, 125
50, 78, 80

Q6.
What is the size of the hypotenuse for a right-angled isosceles triangle with legs of 4 units?

Correct answer: √32
32
16
4
6