# Converging analysis proof

by dancergirlie
Tags: analysis, converging, proof
 P: 200 1. The problem statement, all variables and given/known data Assume that (an) is a bounded (but not necessarily convergent) sequence, and that the sequence (bn) converges to 0. Prove that the sequence (anbn) converges to zero. 2. Relevant equations 3. The attempt at a solution Assume that an is a bounded sequence and bn converges to 0. That means for all n in N, there exists a M >0 so that |an|<=M Since bn converges, that means that it must be bounded as well. Which means for all n in N there exists a P>0 so that |bn|<=P since |an|<=M and |bn|<=P that means for all n in N: |an||bn|<= MP which is equivalent to |anbn|<=MP where MP>0 since M>0 and P>0. Hence (anbn) is bounded Since bn converges to 0 that means for e>0 there exists an N in N so that for n>=N |bn-0|
HW Helper
P: 3,307
 Quote by dancergirlie 1. The problem statement, all variables and given/known data Assume that (an) is a bounded (but not necessarily convergent) sequence, and that the sequence (bn) converges to 0. Prove that the sequence (anbn) converges to zero. 2. Relevant equations 3. The attempt at a solution Assume that an is a bounded sequence and bn converges to 0. That means for all n in N, there exists a M >0 so that |an|<=M Since bn converges, that means that it must be bounded as well. Which means for all n in N there exists a P>0 so that |bn|<=P
an bounded look alright
As bn is convergent, I would say for any P>0, there exists N such that for all n>N then
|bn-0|< |bn|

 Quote by dancergirlie since |an|<=M and |bn|<=P that means for all n in N: |an||bn|<= MP which is equivalent to |anbn|<=MP where MP>0 since M>0 and P>0. Hence (anbn) is bounded Since bn converges to 0 that means for e>0 there exists an N in N so that for n>=N |bn-0|
i think you were almost there...

now what you need to show to prove an.bn converges to zero, is that for any e>0 you can choose N, such that for all n>N you have
|an.bn|<e

as you know an<=M for all n, then
|an.bn|<=|M.bn|

so now you just need to show you can choose N such that for all n>N
|bn|<=e/|M|
and i think you're there
 HW Helper P: 3,307 updated above
 P: 200 Converging analysis proof thanks for the help :)

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