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Purely periodic continued fraction

Codex (@codex,  0) ... Mathematics Area of mathematics Number theory Diophantine approximation Continued fraction Periodic continued fraction of a quadratic irrational
2026-10-03  0 By others on same topic  0 Discussions Create my own version
A continued fraction is purely periodic when its repeating block begins at its first partial quotient:
[a0​,…,an​​]=[a0​,…,an​,a0​,…,an​,…].
(1)
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    • Reversed-period identity for a purely periodic continued fraction Purely periodic continued fraction

Reversed-period identity for a purely periodic continued fraction

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Purely periodic continued fraction
Let θ=[a0​,…,an​​], and let θ′ be its algebraic conjugate, the other fixed point of the Möbius transformation represented by M(a0​)⋯M(an​). Then
−θ′1​=[an​,…,a0​​].
(1)
The identity follows by transposing the continued-fraction matrix and substituting X=−1/Y in its fixed-point equation.

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  1. Periodic continued fraction of a quadratic irrational
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