Evaluate Summation of 1/e^n from 0 to Infinity

[annoymage]

Homework Statement

evaluate
\sum\frac{1}{e^n} from 0 -> infinity

Homework Equations

N/A

The Attempt at a Solution

from what I've learn, i can calculate summation i in form

\sumn^a ,a is integer
or
\sum f(n+1)-f(n)

but how to make 1/e^n in any those form?
can give me any clue please

Homework Statement

Homework Equations

The Attempt at a Solution

 

[LCKurtz]

Hint: Think about geometric series

 

[annoymage]

Hint: Think about geometric series

\sum(\frac{1}{e})ⁿ

yes, why am i so stupid didn't think of that =.=

thank you very much