circle

[andyj]

how do I find the circumfurence of a circle and how do I find the radius from the circumfurence.

[5029]

You have to know one to get the other. The radius is the circumference divided by pi (approx 3.14) and the circumference is the radius multiplied by pi

[TheHitMaker]

Depends on the circle - if it is small enough wind a piece of string round the edge and measure the string - the radius is this length divided by pi as 5029 says - so what's this got to do with history and myth....

[sddsddean]

Both wrong chaps. Circumference = pi * diameter. Diameter = 2 * radius.

[gazzawazza]

The Circumference (C) is found by the formula 2�r (that's 2 x � x r) which is the same as �D as sddsddean says. So, if the radius is 10cm, the sum is 2 x 3.142 x 10 which works out at 62.84.

To find the radius when you know the circumference you divide C by 2�, ie if C = 62.84, then 62.84 divided by 6.284 = 10cm.

[gazzawazza]

Sorry, when I put that little "�" in it was the symbol for pi but it hasn't come out like that!