Suma de la serie 12n(x+1)^(n-1)

   //     1 + x                       \
   ||     -----        for |1 + x| < 1|
   ||        2                        |
   ||       x                         |
   ||                                 |
   ||  oo                             |
12*|< ___                             |
   || \  `                            |
   ||  \            n                 |
   ||  /   n*(1 + x)      otherwise   |
   || /__,                            |
   ||n = 1                            |
   \\                                 /
---------------------------------------
                 1 + x                 

$$\frac{12 \left(\begin{cases} \frac{x + 1}{x^{2}} & \text{for}\: \left|{x + 1}\right| < 1 \\\sum_{n=1}^{\infty} n \left(x + 1\right)^{n} & \text{otherwise} \end{cases}\right)}{x + 1}$$

12*Piecewise(((1 + x)/x^2, |1 + x| < 1), (Sum(n*(1 + x)^n, (n, 1, oo)), True))/(1 + x)