1. Imagine a triangle made by connecting the dots on the circumference or in the centre of the circle.
Without pointing, how can you describe your triangle?

2. Here are some examples.
How would you describe them to your partner without pointing?

3. How many different triangles made by connecting the dots on the circumference or in the centre of the circle can you draw?
How do you know you have got them all?

4. Look at the types of triangle you have. How can you classify them?

5. How did this person classify their triangles?

6. Nothing special about this triangle 
Scalene triangle:
Nothing special about this triangle 

7. Right angled triangle:
1 angle of 90°
Right angled isosceles triangle:
2 other equal angles

8. Equilateral triangle:
All sides equal
All angles are equal – all 60°
Isosceles triangle:
2 equal sides
2 equal angles

9. Isosceles triangle: Two equal sides, two equal angles
Same legs
(sides)
Same feet
(angles)

10. How do you know that this is an isosceles triangle without measuring it?

11. How can I find the angle at the centre in this isosceles triangle?x°

12. One student drew these lines.
What calculation would they do to find the angle, x? x°

13. Another student drew these lines.
What calculation would they do to find the angle, x? x°

14. What calculation would they do to find the angle, x?
Here’s another way.
What calculation would they do to find the angle, x? x°

15. How can I find the other angles in this isosceles triangle?
30° x° x°

16. How can I find the angles in this isosceles triangle?
(Try adding some lines to help)

17. On your whiteboards: Find the missing angles Explain how you found the answer
60° x°
20° x°
50° x°

18. In your books: Find the missing angles

19. Challenge questions

20. On your whiteboards: Draw an isosceles triangle with all acute angles and another

21. On your whiteboards: Draw an isosceles triangle with an obtuse angle and another