Instructables

Circumference of a Circle

Step 2: Diameter

Picture of Diameter
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The distance around a circle is called the circumference. The distance across a circle through the center is called the diameter. is the ratio of the circumference of a circle to the diameter. Thus, for any circle, if you divide the circumference by the diameter, you get a value close to . The picture I have is the relationship, the numbers expressed is the formula:

Where C is circumference and D is diameter. You can test this formula at home with a round dinner plate. If you measure the circumference and the diameter of the plate and then divide C by D, your quotient should come close to Pi . Another way to write this formula is: C = Pi * D where * means multiply. This second formula is commonly used in problems where the diameter is given and the circumference is not known (see the examples below).
 
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