■ベキ和とオイラー・マクローリンの和公式(その7)
オイラー・マクローリンの和公式を
Σ1/k^4
について適用してみたい.
f(x)=1/x^4 f^(5)(x)=−8!/6x^9
f’(x)=−4/x^5 f^(6)(x)=9!/6x^10
f”(x)=20/x^6 f^(7)(x)=−10!/6x^11
f^(3)(x)=−120/x^7 f^(8)(x)=11!/6x^12
f^(4)(x)=840/x^8 f^(9)(x)=−12!/x^13
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Σ(1,n)1/k^4〜∫(1,n)1/x^4dx+(f(n)+f(1))/2+ΣB2k/(2k)!(f^(2k-1)(n)-f^(2k-1)(1))+R
∫(1,n)1/x^4dx=[-1/3x^3]=-1/3n^3+1/3
(f(n)+f(1))/2=(1/n^4+1)/2
(f'(n)-f'(1))/12=(-4/n^5+4)/12
(f^(3)(n)-f^(3)(1))/720=(-120/n^7+120)/720
(f^(5)(n)-f^(5)(1))/30240=(-6720/n^9+6720)/30240
(f^(7)(n)-f^(7)(1))/1209600=(-604800/n^9+60480040)/1209600
Σ1/k^4〜-1/3n^3+1/2n^4-1/3n^5+1/6n^7+・・・+1/3+1/2+1/3-1/12+R
−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
1+1/2^4 =1.0625
1+1/2^4+1/3^4 =1.07485
1+1/2^4+1/3^4+1/4^4 =1.07875
1+1/2^4+1/3^4+1/4^4+1/5^4 =1.08035
1+1/2^4+1/3^4+1/4^4+1/5^4+1/6^4 =1.08112
1+1/2^4+1/3^4+1/4^4+1/5^4+1/6^4+1/7^4 =1.05154
1+1/2^4+1/3^4+1/4^4+1/5^4+1/6^4+1/7^4+1/8^4 =1.08178
1+1/2^4+1/3^4+1/4^4+1/5^4+1/6^4+1/7^4+1/8^4+1/9^4 =1.08194
1+1/2^4+1/3^4+1/4^4+1/5^4+1/6^4+1/7^4+1/8^4+1/9^4+1/10^4=1.08204
π^4/90=1.08232
1/3+1/2+1/3-1/12=1.08333
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