Question

Evaluate the geometric series or state that it diverges.

[infinity]
Σ e^-5n
n=0

Answer 1

sum = = 1 / ( 1-e^(-5) )

( 1.00678 to 5 decimals)

Explanation:

Question: sum

[infinity]

Σ e^-5n

n=0

We note that this is a geometric series,

with n=0, e^(-5n) = e^0 = 1

with n=1, e^(-5n) = e^(-5)

with n=2, e^(-5n) = e^(-10)

...

Therefore the common ratio is r=e^(-5)

and the sum for a geometric series

a+ar+ar^2 + ... ar^N

=a(1-r^(N+1)) / (1-r)

=1(1-r^(infinity-1)) / (1-e^(-5))

= 1 / ( 1-e^(-5) )