1. The Circumference of a Circle
Teaching Mathematics Visually and Actively
The Circumference of a Circle
Tandi Clausen-May

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3. The circumference
of a circle

4. What is  ? First we need  (pi) Is it a number? Is it…..
…...?

5. 
Well… not exactly.
 is a ratio.

6. So  is a bit more than 3. once across twice across three times across
Pi is the number of times you must travel straight across the circle to go the same distance as all the way round the circle.
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once across
twice across
three times across
and a bit further!
So  is a bit more than 3.

7. How can we be sure that  is a bit more than 3?2 1 3
For a regular hexagon, the distance all the way round is exactly 3 times the distance straight across the middle.
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8. Circumference =  × Diameter
And all the way round the circle is a little bit more than all the way round the hexagon.
So all the way round the circle is a little bit more than 3 times straight across the middle.
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Circumference =  × Diameter

9. 2 1 3 Summary Circumference =  × Diameter Circumference =
times the diameter
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…and a little bit more
Circumference =  × Diameter

10. Find it at http://www.uk.sagepub.com
Now watch PP 10-2: The Area of a Circle from the CD inside Teaching Mathematics Visually and Actively
Find it at
Tandi Clausen-May