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Find sum of series 3
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Hong Quy
Yang-Mills Theory
Yang-Mills Theory


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Joined: 20 Feb 2005
Posts: 543
Russian FederationViet Nam

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#1
Find sum of series 3
31.10

\sum_{n=0}^{\infty} \frac{ \cos nx}{ n!}
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PostPosted: Sat Oct 31, 2009 3:24 am  Back to top 
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Kent Merryfield
Birch & Swinnerton Dyer
Birch & Swinnerton Dyer

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Joined: 11 Jun 2004
Posts: 11464
Location: Long Beach, CA
United States

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#2
\sum_{n=0}^{\infty}\frac{\cos nx}{n!}=\text{Re}\,\left(\sum_{n=0}^{\infty}\frac{e^{inx}}{n!}\right)=\text{Re}\,\left(e^{e^{ix...

=\text{Re}\,\left(e^{\cos x+i\sin x}\right)=\text{Re}\,\left(e^{\cos x}(\cos(\sin x)+i\sin(\sin x))\right)=e^{\cos x}\cos(\si...

PostPosted: Sat Oct 31, 2009 10:24 am  Back to top 
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