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