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Sum of series (-1)^nx^n/n!



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  oo           
____           
\   `          
 \         n  n
  \    (-1) *x 
  /    --------
 /        n!   
/___,          
n = 10         
$$\sum_{n=10}^{\infty} \frac{\left(-1\right)^{n} x^{n}}{n!}$$
Sum(((-1)^n*x^n)/factorial(n), (n, 10, oo))
The radius of convergence of the power series
Given number:
$$\frac{\left(-1\right)^{n} x^{n}}{n!}$$
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
$$a_{n} = \frac{1}{n!}$$
and
$$x_{0} = 0$$
,
$$d = 1$$
,
$$c = -1$$
then
$$R = - \lim_{n \to \infty} \left|{\frac{\left(n + 1\right)!}{n!}}\right|$$
Let's take the limit
we find
$$R = -\infty$$
The answer [src]
    /                    2           4         6       8       9        7          5           3                        -x\
 10 |-3628800 - 1814400*x  - 151200*x  - 5040*x  - 90*x  + 10*x  + 720*x  + 30240*x  + 604800*x  + 3628800*x   3628800*e  |
x  *|------------------------------------------------------------------------------------------------------- + -----------|
    |                                                   10                                                          10    |
    \                                                  x                                                           x      /
---------------------------------------------------------------------------------------------------------------------------
                                                          3628800                                                          
$$\frac{x^{10} \left(\frac{10 x^{9} - 90 x^{8} + 720 x^{7} - 5040 x^{6} + 30240 x^{5} - 151200 x^{4} + 604800 x^{3} - 1814400 x^{2} + 3628800 x - 3628800}{x^{10}} + \frac{3628800 e^{- x}}{x^{10}}\right)}{3628800}$$
x^10*((-3628800 - 1814400*x^2 - 151200*x^4 - 5040*x^6 - 90*x^8 + 10*x^9 + 720*x^7 + 30240*x^5 + 604800*x^3 + 3628800*x)/x^10 + 3628800*exp(-x)/x^10)/3628800

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