Correct answer!

We use the .
For the function
f(x) = 2x
x+1
we obtain the limit using l'Hopital's Rule:

lim
x® ¥ 
2x
x+1
=
lim
x® ¥ 
exln(2)
x+1
=
lim
x® ¥ 
ln(2)(2x)
1
= ¥.
Hence

lim
n® ¥ 
2n
n+1
= ¥ ¹ 0.
Therefore, by the the series diverges.

Note that this problem can also be solved using the Ratio Test.