Re: [tmoz:408443] seri sorusu/

e^x   =1+x+x^2/2!+x^3/3!+x^4/4!+.....

e^(-x)=1-x+x^2/2!-x^3/3!+x^4/4!-.... taraf tarafa toplarsak

e^x+e^(-x)=2(1+x^2/2!+x^4/4!+....)

x=1 için

1+1/2!+1/4!+......=(e+e^(-1))/2

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