SOLUTION: The are of a circle is directly proportional to the square of its radius. A circle with a radius of 2cm has an are of 12.566 cm^2. What is the radius of a circle with an area of 78

Question 757962: The are of a circle is directly proportional to the square of its radius. A circle with a radius of 2cm has an are of 12.566 cm^2. What is the radius of a circle with an area of 78.54cm^2?
Round to the nearest unit.
Answer by Cromlix(4381) (Show Source): You can put this solution on YOUR website!
area is directly proportional to
the square of its radius.
A = kr^2
(k is the constant of proportionality)
12.566 = k 2^2
k = 12.566/4
k = 3.1415
Formula: A = 3.1415 r^2
78.54 = 3.1415 r^2
78.54/3.1415 = r^2
r^2 = 25
r = 5cm
Hope this helps.
:-)

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