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How do you find the sum of the geometric series #Sigma 3* 2^(n-1)# from n=1 to 20?

1 Answer

Mar 20, 2017

#3145725#

Explanation:

# sum_(k=1)^n ar^(k-1)= a(r^n -1)/(r -1 )#

# sum_(k=1) ^n 3. 2^(n-1) = 3((2)^20 -1)/(2 -1)# where #a = 3, r# = 2, n = 20#

# sum_(k=1) ^20 = 3((2)^20 -1)/(2 -1)#

#= 3((2)^20 -1)/(2 -1)#

#= 3(1048576 -1)/1#

#= 3(1048575) = 3145725#

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