Problem of the Week

Problem 21

Circle A is a circle of radius r, centre C.

There exists n more circles, each of radius 1 arranged on the outside of Circle A such that each circle of radius 1 touches each of its neighbours and Circle A just once.

Circle B is a circle of centre C, with radius such that it touches each of the circles with radius one exactly once.

i) Find an equation linking the radius of Circle A, r, and the number of circle radius 1. With r as the subject.

Note that the diagram above is just one example, the number of circles can increase.


ii) Circle B is centered at C with radius R = r + 2. It touches each of the n surrounding circles (radius 1) exactly once. All n smaller circles are shaded, while circles A (radius r) and B remain unshaded.

Given that the fraction F of the area of Circle B covered by the shaded circles is:

F = 2412 - 984\sqrt{6} - 1392\sqrt{3} + 1704\sqrt{2},

use an iterative method to estimate the radius ( r ) of Circle A.

Submit a solution!

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