Radius, Diameter, and Circumference

Definition: 

Radius: The distance from a circle’s center to it’s edge. Radius is generally represented with the variable “r”.

Diameter: A straight line going through the center of circle with endpoints on the circle’s edge. A circle’s diameter is equal to twice its radius, given by the formula:
diameter = 2 * radius
[d = 2r]

Circumference: The distance around the edge of a circle; a circle’s perimeter.
Circumference is found using formula: 2 * pi * radius
[C = 2πr]640px-Macro_Circle_01

Example: Find the diameter and circumference of the circle given its radius:

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Solution: 

Use the information provided and the appropriate formulas to find the diameter and circumference.

Step 1: We know the radius of this circle is 6 cm, so we can plug it into the diameter formula:
Diameter = 2 * radius
Diameter = 2 * 6
Diameter = 12

d = 12 cm

Step 2: Using the radius again, we can find the circumference by plugging 6 into the formula:
Circumference = 2 * pi * radius
C = 2π*6
C = 12π = 37.68

C = 37.68 cm

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