Mister Exam

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Sum of series:
1/n^3
1/((3n-2)*(3n+1))
1/(4n^2-9)
n*3^n+1
Identical expressions
(one -cosn)/(n^ two +n- one)
(1 minus co sinus of e of n) divide by (n squared plus n minus 1)
(one minus co sinus of e of n) divide by (n to the power of two plus n minus one)
(1-cosn)/(n2+n-1)
1-cosn/n2+n-1
(1-cosn)/(n²+n-1)
(1-cosn)/(n to the power of 2+n-1)
1-cosn/n^2+n-1
(1-cosn) divide by (n^2+n-1)
Similar expressions
(1+cosn)/(n^2+n-1)
(1-cosn)/(n^2-n-1)
(1-cosn)/(n^2+n+1)

Sum of series (1-cosn)/(n^2+n-1)

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  oo            
____            
\   `           
 \    1 - cos(n)
  \   ----------
  /    2        
 /    n  + n - 1
/___,           
n = 1

$$\sum_{n=1}^{\infty} \frac{1 - \cos{\left(n \right)}}{\left(n^{2} + n\right) - 1}$$

Sum((1 - cos(n))/(n^2 + n - 1), (n, 1, oo))

The rate of convergence of the power series

The graph