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4^n-2*25^n+1/5^4n-2

Sum of series 4^n-2*25^n+1/5^4n-2



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The solution

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  oo                         
____                         
\   `                        
 \    / n       n   1       \
  \   |4  - 2*25  + --*n - 2|
  /   |              4      |
 /    \             5       /
/___,                        
n = 0                        
$$\sum_{n=0}^{\infty} \left(\left(\frac{n}{625} + \left(- 2 \cdot 25^{n} + 4^{n}\right)\right) - 2\right)$$
Sum(4^n - 2*25^n + (1/5)^4*n - 2, (n, 0, oo))
The radius of convergence of the power series
Given number:
$$\left(\frac{n}{625} + \left(- 2 \cdot 25^{n} + 4^{n}\right)\right) - 2$$
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
$$a_{n} = - 2 \cdot 25^{n} + 4^{n} + \frac{n}{625} - 2$$
and
$$x_{0} = 0$$
,
$$d = 0$$
,
$$c = 1$$
then
$$1 = \lim_{n \to \infty} \left|{\frac{2 \cdot 25^{n} - 4^{n} - \frac{n}{625} + 2}{2 \cdot 25^{n + 1} - 4^{n + 1} - \frac{n}{625} + \frac{1249}{625}}}\right|$$
Let's take the limit
we find
False

False

False
The rate of convergence of the power series
The answer [src]
  oo                         
 ___                         
 \  `                        
  \   /      n       n    n \
   )  |-2 + 4  - 2*25  + ---|
  /   \                  625/
 /__,                        
n = 0                        
$$\sum_{n=0}^{\infty} \left(- 2 \cdot 25^{n} + 4^{n} + \frac{n}{625} - 2\right)$$
Sum(-2 + 4^n - 2*25^n + n/625, (n, 0, oo))
The graph
Sum of series 4^n-2*25^n+1/5^4n-2

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