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A193211
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The decimal expansion of the value of r that maximizes the Brahmagupta expression Sqrt((-1+r+r^2+r^3)(1-r+r^2+r^3)(1+r-r^2+r^3)(1+r+r^2-r^3))/4
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1
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1, 6, 5, 3, 7, 4, 5, 5, 1, 5, 0, 7, 7, 7, 7, 1, 9, 2, 9, 7, 0, 7, 9, 0, 6, 2, 3, 8, 3, 6, 6, 4, 5, 9, 7, 1, 4, 5, 6, 6, 2, 2, 3, 0, 7, 0, 2, 5, 1, 8, 4, 1, 6, 9, 2, 7, 0, 1, 1, 0, 5, 2, 0, 2, 9, 4, 6, 5, 6, 8, 6, 4, 8, 0, 8, 8, 3, 1, 8, 2, 7, 2, 1, 5, 6, 9, 3, 1, 5, 1, 6, 5, 0, 1, 3, 9, 8, 5, 9, 5, 7, 8, 9
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OFFSET
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1,2
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COMMENTS
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The area of a convex quadrilateral with fixed sides is maximal when it is organized as a convex cyclic quadrilateral. Furthermore in order that a quadrilateral can have sides in a geometric progression 1:r:r^2:r^3 its common ratio r is limited to the range 1/t<r<t where t is the tribonacci constant (A058265). Consequently when r=1.6537455... it maximizes Brahmagupta's expression for the area of a convex cyclic quadrilateral whose sides form a geometric progression.
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LINKS
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Table of n, a(n) for n=1..103.
Wikipedia, Brahmagupta's formula.
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FORMULA
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r is positive real root of equation 1+r^2+2r^6+5r^8-3r^10=0
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EXAMPLE
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1.653745515077771929707906238366459714566223...
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MATHEMATICA
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RealDigits[r/.NMaximize[{Sqrt[(-1+r+r^2+r^3)(1-r+r^2+r^3)(1+r-r^2+r^3)(1+r+r^2-r^3)]/4, 3/5<r<9/5}, r, AccuracyGoal->120, PrecisionGoal->100, WorkingPrecision->240][[2]]][[1]]
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CROSSREFS
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Sequence in context: A019686 A143304 A021157 * A195713 A109063 A110390
Adjacent sequences: A193208 A193209 A193210 * A193212 A193213 A193214
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KEYWORD
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nonn,cons
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AUTHOR
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Frank M Jackson, Sep 08 2011
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EXTENSIONS
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Mathematica program fixed by Harvey P. Dale, Sep 10 2011
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STATUS
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approved
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