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jmc

geometry junior

Problem

How many inches are in the circumference of a great circle of a sphere which has surface area of sq in? Express your answer in terms of .

Note: To measure the circumference, take the largest circle on the surface of the sphere.
Solution
Let the sphere have radius . A sphere with radius has surface area , so we have Dividing both sides by yields ; taking the square root of both sides and keeping the positive solution yields inches.

A great circle of a sphere is the circular cross-section of the sphere that passes through the sphere's center, which, in this case, is a circle with radius 7. The circumference of this circle is inches.
Final answer
14\pi