**The Circumference of a Circle** is the distance around it. That is, the circumference would be the length of the circle if it were opened up and straightened out to a line segment. The word circumference is used when we are measuring physical objects, as well as when considering abstract geometric forms.

The circumference of a circle is related to one of the most important mathematical constants. This constant, pi, is represented by the Greek letter **π**. Pi is defined as the ratio of a circle’s circumference C to its diameter d.

It is denoted as:

**C=π.d**

**or C= 2π.r**

We will show you examples you both formulas.

**1. Find the circumference of a circle with a radius of 3 cm.**

First, we need to find the diameter. The diameter is twice the radius, so 2 x 3 cm = 6 cm

C = π.d = 6 π

C = 6 x 3.14

C = 18.84 cm or 6 π

**2. You are cutting out a paper to wrap around the edge of a cake you have just baked. The radius of the pie is 5 inches. **

C = 2πr

C = 2π x 5

C = 10π

C = 31.4 inches

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