Radio de convergencia de la serie de potencias
Se da una serie:
$$\frac{n + 1}{n + 3} \left(x + 2\right)^{n}$$
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
$$a_{n} = \frac{n + 1}{n + 3}$$
y
$$x_{0} = -2$$
,
$$d = 1$$
,
$$c = 1$$
entonces
$$R = -2 + \lim_{n \to \infty}\left(\frac{\left(n + 1\right) \left(n + 4\right)}{\left(n + 2\right) \left(n + 3\right)}\right)$$
Tomamos como el límitehallamos
$$R^{1} = -1$$
$$R = -1$$
// 3*x \
// / 2 \ \ || -6 - --- |
||/1 x\ | 2*(2 + x) + 6*x 12*log(-1 - x)| | || log(-1 - x) 2 |
|||- + -|*|------------------- + --------------| for |2 + x| < 1| ||- ----------- + ---------- for And(x >= -3, x < -1)|
||\2 4/ | 4 3 4 | | || 3 2 |
|| \(2 + x) - (2 + x) (2 + x) / | || (2 + x) 3*(2 + x) |
|| | || |
|| oo | || oo |
|< ____ | + |< ____ |
|| \ ` | || \ ` |
|| \ n | || \ n |
|| \ n*(2 + x) | || \ (2 + x) |
|| / ---------- otherwise | || / -------- otherwise |
|| / 3 + n | || / 3 + n |
|| /___, | || /___, |
\\ n = 0 / || n = 0 |
\\ /
$$\begin{cases} \left(\frac{x}{4} + \frac{1}{2}\right) \left(\frac{6 x + 2 \left(x + 2\right)^{2}}{\left(x + 2\right)^{4} - \left(x + 2\right)^{3}} + \frac{12 \log{\left(- x - 1 \right)}}{\left(x + 2\right)^{4}}\right) & \text{for}\: \left|{x + 2}\right| < 1 \\\sum_{n=0}^{\infty} \frac{n \left(x + 2\right)^{n}}{n + 3} & \text{otherwise} \end{cases} + \begin{cases} \frac{- \frac{3 x}{2} - 6}{3 \left(x + 2\right)^{2}} - \frac{\log{\left(- x - 1 \right)}}{\left(x + 2\right)^{3}} & \text{for}\: x \geq -3 \wedge x < -1 \\\sum_{n=0}^{\infty} \frac{\left(x + 2\right)^{n}}{n + 3} & \text{otherwise} \end{cases}$$
Piecewise(((1/2 + x/4)*((2*(2 + x)^2 + 6*x)/((2 + x)^4 - (2 + x)^3) + 12*log(-1 - x)/(2 + x)^4), |2 + x| < 1), (Sum(n*(2 + x)^n/(3 + n), (n, 0, oo)), True)) + Piecewise((-log(-1 - x)/(2 + x)^3 + (-6 - 3*x/2)/(3*(2 + x)^2), (x >= -3)∧(x < -1)), (Sum((2 + x)^n/(3 + n), (n, 0, oo)), True))