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Re: [obm-l] Uma PAG
- To: obm-l@xxxxxxxxxxxxxx
- Subject: Re: [obm-l] Uma PAG
- From: "Marcelo Salhab Brogliato" <msbrogli@xxxxxxxxx>
- Date: Thu, 20 Sep 2007 17:26:27 -0300
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Olá Vitório,
veja que existe um pequeno truque aqui:
Sn = 1 + 2x + 3x^2 + ... + nx^(n-1) = d/dx (x + x^2 + ... + x^n)
Sn = d/dx [ x(x^n-1)/(x-1) ]
agora basta derivar para obter o resultado..
um abraço,
Salhab
On 9/20/07, vitoriogauss <vitoriogauss@xxxxxxxxxx> wrote:
> Calcule a soma Sn=1+2x+3x^2+...+nx^n-1
>
> Eu cheguei ao seguinte resultado:
>
> Sn= (1 - (n+1)x^n + nx^n+1 ) / ( 1 - x )^2
>
> Estou correto????
>
>
>
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