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(4^(n+1)-10^n)/20^n

Sum of series (4^(n+1)-10^n)/20^n



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The solution

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  oo              
____              
\   `             
 \     n + 1     n
  \   4      - 10 
   )  ------------
  /         n     
 /        20      
/___,             
n = 1             
$$\sum_{n=1}^{\infty} \frac{- 10^{n} + 4^{n + 1}}{20^{n}}$$
Sum((4^(n + 1) - 10^n)/20^n, (n, 1, oo))
The radius of convergence of the power series
Given number:
$$\frac{- 10^{n} + 4^{n + 1}}{20^{n}}$$
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
$$a_{n} = - 10^{n} + 4^{n + 1}$$
and
$$x_{0} = -20$$
,
$$d = -1$$
,
$$c = 0$$
then
$$\frac{1}{R} = \tilde{\infty} \left(-20 + \lim_{n \to \infty} \left|{\frac{10^{n} - 4^{n + 1}}{10^{n + 1} - 4^{n + 2}}}\right|\right)$$
Let's take the limit
we find
False

False

$$R = 0$$
The rate of convergence of the power series
The answer [src]
0
$$0$$
0
Numerical answer [src]
6.16297582203915472977912941627e-33
6.16297582203915472977912941627e-33
The graph
Sum of series (4^(n+1)-10^n)/20^n

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