What is the Limit of the Sequence {[(n+3)/(n+1)]^n} as n Approaches Infinity?

Beamsbox
Messages
61
Reaction score
0
Basically,

find the limit of the sequence:

{[(n+3)/(n+1)]^n}, from n=1 to infinity

Book says it's supposed to be e^2, and indeed the graph shows that... I'm not sure what to do with the top of the fraction. Working with the bottom and dividing by n, I obtain, lim as n approaches infinity, (1+(1/n))^n, which is the definition of e... but I'm not sure of the legality of dividing the top and bottom by n, as they're inside the parenthesis to begin with... but if I do it to the top too, I get lim (1+3/n)^n, which I'm not sure what to do with...
lost...

Any help much appreciated!
 
Last edited:
Physics news on Phys.org
Your title is wrong; this isn't an infinite series, it is a sequence. And although it isn't written that way, I assume it is the whole fraction that is raised to the nth power, not just the denominator.

Hint: Do long division on the fraction on the inside to write it as 1 + (..) and try to get it in the form

(1 + 1/t)t.
 
Right, nice assumption, edited and fixed. Long division, I knew I needed it in the form ofthe definition of e, but didn't know how... I'll check it out. Thanks for the help.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
Back
Top