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18 votes
18 votes
4. What is the circumference of a circle whose area is 81π cm squared?

User Tinister
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2 Answers

25 votes
25 votes
Area = pi*r^2
Circumference = 2pi*r

Step 1: find the radius from area
81pi=pi*r^2
81=r^2
9=r

Step 2: plug in radius to the circumference equation

Circumference = 2pi*r

18pi is the answer, otherwise know as 56.52 as well.
User Chris Edgington
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2.6k points
12 votes
12 votes

Explanation:

Let us assume R be the radius of circle We know that, area of circle = πR2 81πr2 = πR2 R = √81 r R = 9r Circumference = 2 πr = 2 π (9r) = 18πr

User Minhaz
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3.8k points