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What is ratio of areas of circumcircle and in circle of a square?

  • A.1 : 2
  • B.1 : 3
  • C.3 : 1
  • D.2 : 1

Answer: D

For a square of side \(a\), the circumcircle passes through the vertices and has the diagonal as its diameter, and the incircle touches the sides and has the side as its diameter.

\[ R = \frac{a\sqrt{2}}{2},\qquad r = \frac{a}{2} \]

\[ \frac{\pi R^2}{\pi r^2} = \frac{a^2/2}{a^2/4} = 2 \]

So the areas are in the ratio 2 : 1. The ratio of the radii is \(\sqrt{2} : 1\), so the ratio of the areas is the square of that. The ratios 1 : 2 and 1 : 3 are not correct, and 3 : 1 is not either. The answer is 2 : 1, option D.

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