Monday, 18 June 2018

Limit of fracn1/25logn



I have to show that the limit of n1/25logn is equal to as n goes to infinity.



I have seen in some cases people using logarithms on the numerator and the denominator and say that the original fraction goes to infinity(or zero) if the logarithms go to infinity (or zero). Is this valid? And when it does not work? For example, in this case if i work with the logarithms it comes out to be a non zero constant, so this approach is wrong.
L'hospital on the other hand doesn't seem practical. Any ideas?



Answer



logn1/25logn=12lognlog5logn



since 12<log5, then use the continuity of log(x) to conclude that n1/25logn0



Using logarithms respectively on the numerator and the denominator lead to possible mistakes, such as to say:



log1nlog1n212, so 1n1n2e12, which is obviously wrong.


No comments:

Post a Comment

real analysis - How to find limhrightarrow0fracsin(ha)h

How to find lim without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...