June 1st, 2017, 06:25 PM  #1 
Member Joined: Jan 2017 From: California Posts: 62 Thanks: 5  sequence convergence
Hi guys, is it safe to assume that this sequence $$a_{n}=\sqrt{\frac{125n^3+7n}{5n^3+7n^2}}$$ diverges since the nth term test leads to a limit equal to 5? Thanks. Last edited by skipjack; June 1st, 2017 at 09:47 PM. 
June 1st, 2017, 06:28 PM  #2 
Math Team Joined: Dec 2013 From: Colombia Posts: 6,778 Thanks: 2195 Math Focus: Mainly analysis and algebra 
Well, if the terms tend to 5, doesn't that mean that the sequence converges (to 5)? The series $\sum a_n$ would diverge though. 
June 1st, 2017, 06:50 PM  #3 
Member Joined: Jan 2017 From: California Posts: 62 Thanks: 5  The limit of the nth term is equal to 5. I thought the series diverges anytime that limit is different from 0. That's why I concluded that it diverged.
Last edited by skipjack; June 1st, 2017 at 09:48 PM. 
June 1st, 2017, 06:54 PM  #4 
Member Joined: Jan 2017 From: California Posts: 62 Thanks: 5  Ok, I just understood what you meant... thanks again.
Last edited by skipjack; June 1st, 2017 at 09:49 PM. 
June 1st, 2017, 08:40 PM  #5 
Senior Member Joined: Aug 2012 Posts: 1,373 Thanks: 322  In your OP, you called it a sequence. That's just the list of terms. The series is the sum. Two different things. Remember: The sum of the series is defined as the limit of the sequence of partial sums.
Last edited by skipjack; June 1st, 2017 at 09:50 PM. 

Tags 
convergence, sequence 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Convergence of a sub sequence  Lalitha183  Real Analysis  2  May 15th, 2017 03:39 AM 
Sequence convergence (Leibniz and absolute convergence)  Chemist@  Calculus  7  November 1st, 2014 02:16 PM 
Convergence of a sequence  martemac  Calculus  2  March 9th, 2013 10:33 AM 
Convergence of a sequence  martemac  Real Analysis  9  March 9th, 2013 10:29 AM 
convergence of a sequence  sis3  Real Analysis  1  May 4th, 2010 11:11 AM 