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Problem 19 - Entrance Test

If the circumference of a circle is 10π, what is the area of the largest square that can be inscribed in the circle?

Correct: B

First, find the radius of the circle from its circumference. C = 2πr 10π = 2πr r = 5 When a square is inscribed in a circle, the diagonal of the square is equal to the diameter of the circle. Diameter d = 2r = 2 * 5 = 10. Let 's' be the side length of the square. By the Pythagorean theorem, the diagonal of a square is s*sqrt(2). So, s*sqrt(2) = 10 s = 10 / sqrt(2) s = (10*sqrt(2)) / 2 s = 5*sqrt(2) The area of the square is A = s^2. A = (5*sqrt(2))^2 A = 5^2 * (sqrt(2))^2 A = 25 * 2 A = 50 square units.