Circles and a Square

Geometry Level 2

A small circle with radius 3 is enclosed by square which is also enclosed by a bigger circle.

The ratio between the bigger circle and the smaller circle's circumference can be expressed as n \sqrt{n} . What is the value of n n ?


The answer is 2.

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1 solution

The side length of the square which is also the diameter of the small circle is twice the radius of the small circle and it is 2 × 3 = 6 2 \times 3 = 6 . The diameter of the big circle which is also the diagonal of the square can be found by using the pythagorean theorem and it is 6 2 6\sqrt{2} . Now that we know the diameter of the small and the big circle, we need to find their circumferences. The circumference of a circle is given by c = π d c=\pi d where d d is the diameter of the circle. By using the formula, the circumference of the small circle is 6 π 6\pi and the big circle is 6 π 2 6\pi \sqrt{2} . To find the ratio of the circumference of the bog circle to the circumference of the small circle, we need to divide

r a t i o = c i r c u m f e r e n c e o f t h e b i g c i r c l e c i r c u m f e r e n c e o f t h e s m a l l c i r c l e = 6 π 2 6 π = 2 ratio=\dfrac{circumference~of~the~big~circle}{circumference~of~the~small~circle}=\dfrac{6\pi \sqrt{2}}{6\pi}=\sqrt{2}

It is of the form n \sqrt{n} as required in the problem. The required answer is 2 \boxed{2} .

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