posted by relle on .
Hi. I'm having trouble with the summation of n from i=2 of ((2^n-i)(2^n)). Any help would be greatly appreciated!
the way I am reading the question you have i is going from 2 to n
so there will be n-1 terms
using i = 2,3,4,..,n
I get 2^(2n-2) + 2^(2n-2) + ...
Sum of n terms of a geometric series is
a(1 - r^n)/(1-r)
so a= 2^(2n-2), r = 2^(-1) and the number of terms is n-1
and the sum is
2^(2n-2)[1 - 2^(-1)] / 1-2^(-1))
=2^(n-1)(2^n - 1)