In: Advanced Math
1. a.) Find the values of x for which the series converges. Express your answer in interval notation. n = 1 ∞ ∑(−3)n?n
b.) Find the sum of the series (valid over the values of x found in part a).
1.
(a). Given series 
 .
If  
be the radius of convegence of the above series then ,




Now at 
 the series is  
which is an divergent series .
At  
   the
series is  
  
which is an divergent series .
Hence the interval of convergence of the given series is
 .
Answer : 
 .
(b). Sum of the series , 

, which is an geometric series with common ratio -3x .



, as  
.

Hence the required sumof the series is  
.
Answer : 
 .
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If you have doubt or need more clarification at any step please comment .