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Sequence with Fibonacci numbers - IMO LongList 1992 USA1

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September 2, 2010
FibonacciFibonacci sequencelimitSequenceIMO ShortlistIMO Longlistcalculus

Problem Statement

Let FnF_n be the nth Fibonacci number, defined by F1=F2=1F_1 = F_2 = 1 and Fn=Fn1+Fn2F_n = F_{n-1} + F_{n-2} for n>2n > 2. Let A0,A1,A2,A_0, A_1, A_2,\cdots be a sequence of points on a circle of radius 11 such that the minor arc from Ak1A_{k-1} to AkA_k runs clockwise and such that μ(Ak1Ak)=4F2k+1F2k+12+1\mu(A_{k-1}A_k)=\frac{4F_{2k+1}}{F_{2k+1}^2+1} for k1k \geq 1, where μ(XY)\mu(XY ) denotes the radian measure of the arc XYXY in the clockwise direction. What is the limit of the radian measure of arc A0AnA_0A_n as nn approaches infinity?