Impossible triangles

In this lesson, we will determine when it is impossible to construct a triangle given three lengths.

This quiz includes images that don't have any alt text - please contact your teacher who should be able to help you with an audio description.

Quiz:

Intro quiz - Recap from previous lesson

Before we start this lesson, let’s see what you can remember from this topic. Here’s a quick quiz!

Q1.If you know the length of the sides of a triangle, you can _______ it using a pair of ______.

1/5

Q2.This circle is drawn on a centimetre square grid. State the radius and diameter.

2/5

Q3.This circle is drawn on a centimetre square grid. State the radius and diameter.

3/5

Q4.This circle is drawn on a centimetre square grid. State the radius and diameter.

4/5

Q5.Two students were asked to construct a triangle with side lengths 3 cm , 2 cm and 4 cm. Are they both correct?

5/5

This quiz includes images that don't have any alt text - please contact your teacher who should be able to help you with an audio description.

Quiz:

Intro quiz - Recap from previous lesson

Before we start this lesson, let’s see what you can remember from this topic. Here’s a quick quiz!

Q1.If you know the length of the sides of a triangle, you can _______ it using a pair of ______.

1/5

Q2.This circle is drawn on a centimetre square grid. State the radius and diameter.

2/5

Q3.This circle is drawn on a centimetre square grid. State the radius and diameter.

3/5

Q4.This circle is drawn on a centimetre square grid. State the radius and diameter.

4/5

Q5.Two students were asked to construct a triangle with side lengths 3 cm , 2 cm and 4 cm. Are they both correct?

5/5

Video

Click on the play button to start the video. If your teacher asks you to pause the video and look at the worksheet you should:

  • Click "Close Video"
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Your video will re-appear on the next page, and will stay paused in the right place.

Worksheet

These slides will take you through some tasks for the lesson. If you need to re-play the video, click the ‘Resume Video’ icon. If you are asked to add answers to the slides, first download or print out the worksheet. Once you have finished all the tasks, click ‘Next’ below.

This quiz includes images that don't have any alt text - please contact your teacher who should be able to help you with an audio description.

Quiz:

Impossible triangles Quiz

Don’t worry if you get a question wrong! Forgetting is an important step in learning. We will recap next lesson.

Q1.When constructing a triangle, should you erase the construction lines at the end?

1/5

Q2.Which triangle is impossible to construct?

2/5

Q3.What equipment would you use to construct a 9cm, 7cm, 18cm triangle correctly?

3/5

Q4.Which triangle is impossible to construct?

4/5

Q5.How do I know from the construction that this is an impossible triangle?

5/5

This quiz includes images that don't have any alt text - please contact your teacher who should be able to help you with an audio description.

Quiz:

Impossible triangles Quiz

Don’t worry if you get a question wrong! Forgetting is an important step in learning. We will recap next lesson.

Q1.When constructing a triangle, should you erase the construction lines at the end?

1/5

Q2.Which triangle is impossible to construct?

2/5

Q3.What equipment would you use to construct a 9cm, 7cm, 18cm triangle correctly?

3/5

Q4.Which triangle is impossible to construct?

4/5

Q5.How do I know from the construction that this is an impossible triangle?

5/5

Lesson summary: Impossible triangles

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Time to move!

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For 5 mins...

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