■ある無限級数(その163)

1/(1^2+a^2) + 1/(3^2+ a^2) + 1/(5^2+ a^2) + ・・

=(π/(4a))・(e^(aπ)-1)/( e^(aπ)+1)

a=qi/pを代入すると

左辺=1/(1^2−q^2/p^2)+1/(3^2−q^2/p^2)+1/(5^2−q^2/p^2)+・・・

=1/(1^2−q^2/p^2)+1/(3^2−q^2/p^2)+1/(5^2−q^2/p^2)+・・・

=p/2q{{1/(1−q/p)−1/(1+q/p)}+{1/(3−q/p)−1/(3+q/p)}+{1/(5−q/p)−1/(5+q/p)}+・・・}

=p/2q{{1/(p−q)/p)−1/((p+q)/p)}+{1/(3p−q)/p)−1/(3p+q)/p)}+{1/(5p−q)/p)−1/(5p+q)/p)}+・・・}

=p^2/2q{{1/(p−q)−1/(p+q)}+{1/(3p−q)−1/(3p+q)}+{1/(5p−q)−1/(5p+q)}+・・・}

右辺=(π/(4a))・(e^(aπ)-1)/( e^(aπ)+1)

=|πp/4q・tan(qπ/2p)|

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[1]p=4,q=3

左辺=16/6{{1/1−1/7}+{1/9−1/15}+{1/17−1/23}+・・・}

右辺=π/3・tan(3π/8)

B=1/1−1/7+1/9−1/15+1/17−1/23+・・・

=π/8・tan(3π/8)

[2]p=4,q=1

左辺=8{{1/3−1/5}+{1/11−1/13}+{1/19−1/21}+・・・}

右辺=π・tan(π/8)

C=1/3−1/5+1/11−1/13+1/19−1/21+・・・

=π/8・tan(π/8)

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