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The​ ​Circle​ ​-​ ​Basics
What​ ​is​ ​a​ ​circle?

Terms​:
Circumference​ ​-​ ​The​ ​length​ ​around​ ​the​ ​outside​ ​of​ ​the​ ​circle
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Always​ ​passes​ ​through​ ​the​ ​middle!
Radius​ ​-​ ​The​ ​length​ ​from​ ​the​ ​centre​ ​of​ ​the​ ​circle​ ​to​ ​the​ ​edge
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But…​ ​how​ ​do​ ​we​ ​find​ ​them?
This​ ​is​ ​where​ ​Pi​ ​comes​ ​in
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​ ​It​ ​is​ ​a​ ​mathematical​ ​constant
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​
Pi​ ​is​ ​written​ ​as​ ​π,​ ​which​ ​is​ ​a​ ​Greek​ ​letter
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14​ ​(scroll​ ​down​ ​for​ ​Pi​ ​to​ ​100​ ​decimal
places)
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So​ ​you​ ​would​ ​do:
C=πd
Sub​ ​the​ ​values​ ​in
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14​ ​x​ ​5
Circumference​ ​=​ ​15
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So​ ​you​ ​would​ ​do:
A=πr2​ ​(r​ ​squared)
Sub​ ​the​ ​values​ ​in
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14​ ​x​ ​100
Area​ ​=​ ​314​ ​cm
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First,​ ​you​ ​need​ ​the​ ​formula​ ​you​ ​used​ ​earlier:

C=πd

Example
Calculate​ ​the​ ​diameter​ ​of​ ​a​ ​circle​ ​with​ ​a​ ​circumference​ ​of​ ​8m
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8=3
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14
D=​ ​2
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D=​ ​2
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Just​ ​half​​ ​the​ ​diameter!
Pi​ ​to​ ​100​ ​decimal​ ​places
3
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