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Example Question #16 : Circles
Circle B has a circumference of 36π. What is the area of circle A, which has a radius half the length of the radius of circle B?
Possible Answers:
18π
324π
9π
81π
18
Correct answer:
81π
Explanation:
To find the radius of circle B, use the circumference formula (c = πd = 2πr):
2πr = 36π
Divide each side by 2π: r = 18
Now, if circle A has a radius half the length of that of B, A's radius is 18 / 2 = 9.
The area of a circle is πr2. Therefore, for A, it is π*92 = 81π.
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