Question

How we can evaluate this : ∑2ⁿ from k=1 to n , as n→-∞ ?

Answer 1

`sum""_(k=1)^(n->-oo) =4`

Explanation:

The series is just
`2 + 1 + 1/2 + 1/4 + ...`
That is a geometric series with
`a=2, r=1/2`
So the sum is `a/(1-r) = 2/(1-1/2)`