How do you find the circumference and area of a circle with diameter of 18 inches?

1 Answer
Ken C.
Sep 29, 2015

Circumference = #18pi# (56.52 inches) and area = #81pi# (254.34 inches)

Explanation:

We use the following formulas: #C = 2pir# and #A = pir^2#, where #C# is circumference, #A# is area, and #r# is the radius (half the diameter).

First step is finding the radius. As I mentioned above, the radius is half the diameter, or in this case, half of 18. So, our radius is 9 inches. Now we can apply our formulas; we'll start with circumference:

#C = 2pir#
#C = 2pi*9#
#C = 18pi#, or approximately 56.52 inches (remember that #pi ~= 3.14#)

For area:

#A = pir^2#
#A = pi*(9)^2#
#A = 81pi#, or approximately 254.34 inches

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