The Limit Comparison Test

Given N, if  
an,bn > 0  for all n > N, then

if  

lim
n® ¥ 
an
bn
   = L  where L is finite and positive
then either both series  
   ¥
å
n = 1 
an  and   ¥
å
n = 1 
bn  converge  or  they  both  diverge.

if  

lim
n® ¥ 
an
bn
= 0  and   ¥
å
n = 1 
bn  converges  then   ¥
å
n = 1 
an  also  converges

and if  

lim
n® ¥ 
an
bn
= ¥  and   ¥
å
n = 1 
bn  diverges  then   ¥
å
n = 1 
an  also  diverges