1. The circumference of a circle
Circle Formulae 1
The circumference of a circle
Tandi Clausen-May
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2. Click the mouse only when you see or
If you click too soon you will miss the best bits.
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Click to see
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3. The circumference
of a circle
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Tandi Clausen-May

4. What is  ? First we need  (pi) Is it a number? Is it…..
…..?
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5. 
Well… not exactly.
 is a ratio.
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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.
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7. How can we be sure that  is a bit more than 3?2 1
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
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9. Summary
Circumference
=  × Diameter
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10. Now watch
Circle Formulae 2
The area of a circle
Tandi Clausen-May