Geometry, Algebra, Combinatorics, MIXED?

Algebra Level 5

Let C 0 , C 1 , C 2 , . . . C_{0}, C_{1}, C_{2},... be a sequence of circles in the Cartesian plane defined as:

  1. C 0 C_{0} is the circle x 2 + y 2 = 1 x^{2} + y^{2} = 1
  2. For n = 0 , 1 , 2 , 3 , . . . n = 0, 1, 2, 3, ... , the circle C n + 1 C_{n+1} lies in the upper half plane and is tangent to C n C_{n} as well as both branches of the hyperbola x 2 y 2 = 1 x^{2} - y^{2} = 1

Let r n r_{n} be the radius of C n C_{n} . Find the length of r 10 r_{10}

Please use Wolfram Alpha only in the last step. This is a modified APMO problem.


The answer is 22619537.

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1 solution

Bob Kadylo
Jul 27, 2018

Consider OEIS A001541 as a " hint " to the method I used.

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