# Impossible triangles

## Lesson details

### Key learning points

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

### Licence

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## Video

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## Worksheet

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## Starter quiz

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### 5 Questions

Q1.
If you know the length of the sides of a triangle, you can _______ it using a pair of ______.
construct, protractor
draw, compass
make,ruler
Q2.
This circle is drawn on a centimetre square grid. State the radius and diameter.
Radius = 2cm, Diameter = 2cm
Radius = 4cm, Diameter = 2cm
Q3.
This circle is drawn on a centimetre square grid. State the radius and diameter.
Correct answer: R = 1cm, D = 2cm
R = 1cm; D = 1cm
R = 2cm; D = 1cm
Q4.
This circle is drawn on a centimetre square grid. State the radius and diameter.
Others
R = 4cm, D = 4cm
Correct answer: R = 4cm, D = 8cm.
R= 8cm, D = 4cm
Q5.
Two students were asked to construct a triangle with side lengths 3 cm , 2 cm and 4 cm. Are they both correct?
No, they are not both correct. Only B is correct because she mentioned the shortest angle first then measured the rest.
No, they are not both correct. Only student A is correct because the base is 3cm.
Correct answer: Yes, they are both correct because both of the triangles are identical (congruent) but they are orientated differently.

## Exit quiz

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### 5 Questions

Q1.
When constructing a triangle, should you erase the construction lines at the end?
Some of them
Yes
Q2.
Which triangle is impossible to construct?
6cm, 8cm, 3cm
7cm, 3cm, 9cm
All of them
Q3.
What equipment would you use to construct a 9cm, 7cm, 18cm triangle correctly?
Ruler and pencil
Correct answer: Ruler, pencil and compass
Ruler, pencil and protractor
Q4.
Which triangle is impossible to construct?
1cm, 1cm, 1cm
6cm, 2cm, 5cm