The area of a square is 𝑑. What is the area of the circle which has the…

2018

The area of a square is 𝑑. What is the area of the circle which has the diagonal of the square as its diameter?

Answer: D. 1/2 𝜋𝑑Solution: Derive the circle area from the square's area step by step. Let the side length of the square be s. Since the square's area is d, we have s = √d.…

  1. A.

    𝜋𝑑

  2. B.

    𝜋𝑑^2

  3. C.

    1/4 𝜋𝑑^2

  4. D.

    1/2 𝜋𝑑

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Correct answer: D

Solution: Derive the circle area from the square's area step by step.

  • Let the side length of the square be s. Since the square's area is d, we have s = √d.

  • The diagonal of the square is s·√2 = √d · √2 = √(2d). This diagonal is the circle's diameter.

  • Radius of the circle r = (diameter)/2 = √(2d)/2.

  • Area of the circle = π·r² = π·(√(2d)/2)² = π·(2d)/4 = (1/2)·π·d.

Therefore the area of the circle is (1/2)·π·d.

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