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Alternating Series Sum

Compute the infinite sum $ S, $ where \[S = \frac{1}{2} - \frac{2}{4} + \frac{3}{8} - \frac{4}{16} + \frac{5}{32} - \dots + \frac{n}{2^n} (-1)^{n + 1} + \dotsb.\]

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$\frac{a}{b}$
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0
=
%

$a^n$
$a^{\circ}$
$a_n$
$\sqrt{}$
$\sqrt[n]{}$
$\pi$
$\ln{}$
$\log$
$\theta$
$\sin{}$
$\cos{}$
$\tan{}$

$($
$)$
$[$
$]$
$\cap$
$\cup$
$,$
$\infty$