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