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Sum of series arctg(x^3)/(n(n+2)(n+3))



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The solution

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  oo                   
____                   
\   `                  
 \             / 3\    
  \        atan\x /    
  /   -----------------
 /    n*(n + 2)*(n + 3)
/___,                  
n = 1                  
$$\sum_{n=1}^{\infty} \frac{\operatorname{atan}{\left(x^{3} \right)}}{n \left(n + 2\right) \left(n + 3\right)}$$
Sum(atan(x^3)/(((n*(n + 2))*(n + 3))), (n, 1, oo))
The radius of convergence of the power series
Given number:
$$\frac{\operatorname{atan}{\left(x^{3} \right)}}{n \left(n + 2\right) \left(n + 3\right)}$$
It is a series of species
$$a_{n} \left(c x - x_{0}\right)^{d n}$$
- power series.
The radius of convergence of a power series can be calculated by the formula:
$$R^{d} = \frac{x_{0} + \lim_{n \to \infty} \left|{\frac{a_{n}}{a_{n + 1}}}\right|}{c}$$
In this case
$$a_{n} = \frac{\operatorname{atan}{\left(x^{3} \right)}}{n \left(n + 2\right) \left(n + 3\right)}$$
and
$$x_{0} = 0$$
,
$$d = 0$$
,
$$c = 1$$
then
$$1 = \lim_{n \to \infty}\left(\frac{\left(n + 1\right) \left(n + 4\right)}{n \left(n + 2\right)}\right)$$
Let's take the limit
we find
True

False
The answer [src]
      / 3\
5*atan\x /
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    36    
$$\frac{5 \operatorname{atan}{\left(x^{3} \right)}}{36}$$
5*atan(x^3)/36

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