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Suma de la serie (-1)^n*2^(n+1)*(x-1)^(3*n)/(((2*n+1)*(n+2)*(3*n+1)))



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Solución

Ha introducido [src]
  oo                             
____                             
\   `                            
 \          n  n + 1        3*n  
  \     (-1) *2     *(x - 1)     
  /   ---------------------------
 /    (2*n + 1)*(n + 2)*(3*n + 1)
/___,                            
n = 0                            
$$\sum_{n=0}^{\infty} \frac{\left(-1\right)^{n} 2^{n + 1} \left(x - 1\right)^{3 n}}{\left(n + 2\right) \left(2 n + 1\right) \left(3 n + 1\right)}$$
Sum((((-1)^n*2^(n + 1))*(x - 1)^(3*n))/((((2*n + 1)*(n + 2))*(3*n + 1))), (n, 0, oo))
Radio de convergencia de la serie de potencias
Se da una serie:
$$\frac{\left(-1\right)^{n} 2^{n + 1} \left(x - 1\right)^{3 n}}{\left(n + 2\right) \left(2 n + 1\right) \left(3 n + 1\right)}$$
Es la serie del tipo
$$a_{n} \left(c x - x_{0}\right)^{d n}$$
- serie de potencias.
El radio de convergencia de la serie de potencias puede calcularse por la fórmula:
$$R^{d} = \frac{x_{0} + \lim_{n \to \infty} \left|{\frac{a_{n}}{a_{n + 1}}}\right|}{c}$$
En nuestro caso
$$a_{n} = \frac{\left(-1\right)^{n} 2^{n + 1}}{\left(n + 2\right) \left(2 n + 1\right) \left(3 n + 1\right)}$$
y
$$x_{0} = 1$$
,
$$d = 3$$
,
$$c = 1$$
entonces
$$R^{3} = 1 + \lim_{n \to \infty}\left(\frac{2^{- n - 2} \cdot 2^{n + 1} \left(n + 3\right) \left(2 n + 3\right) \left(3 n + 4\right)}{\left(n + 2\right) \left(2 n + 1\right) \left(3 n + 1\right)}\right)$$
Tomamos como el límite
hallamos
$$R^{3} = \frac{3}{2}$$
$$R = 1.14471424255333$$
Respuesta [src]
  //                                                                                                 -pi*I     /                          pi*I\           pi*I    /                          5*pi*I\              /                          pi*I\              /                          3*pi*I\                        \
  ||                                                      /             ___________      \           ------    |             ___________  ----|           ----    |             ___________  ------|              |             ___________  ----|              |             ___________  ------|                        |
  ||                  /              3  pi*I\      2/3    |    3 ___ 3 /         3   pi*I|      2/3    3       |    3 ___ 3 /         3    3  |      2/3   3      |    3 ___ 3 /         3     3   |       ___    |      ___   /         3    2  |       ___    |      ___   /         3     2   |                        |
  ||     1         log\1 - 2*(-1 + x) *e    /   3*2   *log\1 - \/ 2 *\/  (-1 + x)  *e    /   3*2   *e      *log\1 - \/ 2 *\/  (-1 + x)  *e    /   3*2   *e    *log\1 - \/ 2 *\/  (-1 + x)  *e      /   I*\/ 2 *log\1 - \/ 2 *\/  (-1 + x)  *e    /   I*\/ 2 *log\1 - \/ 2 *\/  (-1 + x)  *e      /        |        3|     |
  ||------------ - -------------------------- + ------------------------------------------ - -------------------------------------------------- - -------------------------------------------------- - ------------------------------------------- + ---------------------------------------------  for 2*|(-1 + x) | <= 1|
  ||           3                     6                            ___________                                      ___________                                          ___________                                       ___________                                    ___________                                      |
  ||30*(-1 + x)           60*(-1 + x)                          3 /         3                                    3 /         3                                        3 /         3                                       /         3                                    /         3                                       |
  ||                                                        10*\/  (-1 + x)                                  10*\/  (-1 + x)                                      10*\/  (-1 + x)                                    3*\/  (-1 + x)                                 3*\/  (-1 + x)                                        |
  ||                                                                                                                                                                                                                                                                                                                      |
2*|<                                                                                                                                  oo                                                                                                                                                                                  |
  ||                                                                                                                                ____                                                                                                                                                                                  |
  ||                                                                                                                                \   `                                                                                                                                                                                 |
  ||                                                                                                                                 \          n  n         3*n                                                                                                                                                          |
  ||                                                                                                                                  \     (-1) *2 *(-1 + x)                                                                                                                                                             |
  ||                                                                                                                                   )  -----------------------                                                                                                                                         otherwise       |
  ||                                                                                                                                  /          3              2                                                                                                                                                         |
  ||                                                                                                                                 /    2 + 6*n  + 11*n + 17*n                                                                                                                                                          |
  ||                                                                                                                                /___,                                                                                                                                                                                 |
  \\                                                                                                                                n = 0                                                                                                                                                                                 /
$$2 \left(\begin{cases} - \frac{\sqrt{2} i \log{\left(- \sqrt{2} \sqrt{\left(x - 1\right)^{3}} e^{\frac{i \pi}{2}} + 1 \right)}}{3 \sqrt{\left(x - 1\right)^{3}}} + \frac{\sqrt{2} i \log{\left(- \sqrt{2} \sqrt{\left(x - 1\right)^{3}} e^{\frac{3 i \pi}{2}} + 1 \right)}}{3 \sqrt{\left(x - 1\right)^{3}}} - \frac{3 \cdot 2^{\frac{2}{3}} e^{- \frac{i \pi}{3}} \log{\left(- \sqrt[3]{2} \sqrt[3]{\left(x - 1\right)^{3}} e^{\frac{i \pi}{3}} + 1 \right)}}{10 \sqrt[3]{\left(x - 1\right)^{3}}} + \frac{3 \cdot 2^{\frac{2}{3}} \log{\left(- \sqrt[3]{2} \sqrt[3]{\left(x - 1\right)^{3}} e^{i \pi} + 1 \right)}}{10 \sqrt[3]{\left(x - 1\right)^{3}}} - \frac{3 \cdot 2^{\frac{2}{3}} e^{\frac{i \pi}{3}} \log{\left(- \sqrt[3]{2} \sqrt[3]{\left(x - 1\right)^{3}} e^{\frac{5 i \pi}{3}} + 1 \right)}}{10 \sqrt[3]{\left(x - 1\right)^{3}}} + \frac{1}{30 \left(x - 1\right)^{3}} - \frac{\log{\left(- 2 \left(x - 1\right)^{3} e^{i \pi} + 1 \right)}}{60 \left(x - 1\right)^{6}} & \text{for}\: 2 \left|{\left(x - 1\right)^{3}}\right| \leq 1 \\\sum_{n=0}^{\infty} \frac{\left(-1\right)^{n} 2^{n} \left(x - 1\right)^{3 n}}{6 n^{3} + 17 n^{2} + 11 n + 2} & \text{otherwise} \end{cases}\right)$$
2*Piecewise((1/(30*(-1 + x)^3) - log(1 - 2*(-1 + x)^3*exp_polar(pi*i))/(60*(-1 + x)^6) + 3*2^(2/3)*log(1 - 2^(1/3)*((-1 + x)^3)^(1/3)*exp_polar(pi*i))/(10*((-1 + x)^3)^(1/3)) - 3*2^(2/3)*exp(-pi*i/3)*log(1 - 2^(1/3)*((-1 + x)^3)^(1/3)*exp_polar(pi*i/3))/(10*((-1 + x)^3)^(1/3)) - 3*2^(2/3)*exp(pi*i/3)*log(1 - 2^(1/3)*((-1 + x)^3)^(1/3)*exp_polar(5*pi*i/3))/(10*((-1 + x)^3)^(1/3)) - i*sqrt(2)*log(1 - sqrt(2)*sqrt((-1 + x)^3)*exp_polar(pi*i/2))/(3*sqrt((-1 + x)^3)) + i*sqrt(2)*log(1 - sqrt(2)*sqrt((-1 + x)^3)*exp_polar(3*pi*i/2))/(3*sqrt((-1 + x)^3)), 2*Abs((-1 + x)^3) <= 1), (Sum((-1)^n*2^n*(-1 + x)^(3*n)/(2 + 6*n^3 + 11*n + 17*n^2), (n, 0, oo)), True))

    Ejemplos de hallazgo de la suma de la serie