Saturday, 8 March 2014

real analysis - What is limxto0log0(x)?



As per the title; what is lim ?



According to WolframAlpha: \lim_{x \to 0} \log_0(x) = 0 but how is this possible?



Surely the limit should be indeterminate since \log_0(x) = \frac{\log(x)}{\log(0)} and \log(0) = indeterminate?


Answer



\lim\limits_{x\to0}\log_0 x cannot exist unless \log_0 x exists for x in some open neighborhood of 0, with the possible exception of x=0. (Since the base must be positive, we can take "open neighborhood of 0" to mean a set of the form [0,\varepsilon) where \varepsilon>0.)




Later edit: I suspect what's going on is something like this:
\log_\varepsilon x = \frac{\log x}{\log\varepsilon},
then letting \varepsilon\downarrow0, we have the denominator going to -\infty, so that the fraction approaches 0. Hence \log_0 x get construed to be 0, and then one lets x go to 0, and the limit is 0.


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