Monday, November 6, 2017

real analysis - Limit of dfractln(1+t) without L'Hospital




I'm trying to prove: limt0tln(1+t)=1 without use L'Hospital and derivate, because I still do not define derived from the logarithm, is there any way to prove it by the definition epsilon-delta? So far I have only defined log as the inverse function of ax and particular case a=e although the latter is proposed very weak, it may be improved later using integrals, some help thanks in advance.



Answer



limx0ln(1+x)x=limx01xln(1+x)=limx0ln((1+x)1x)=ln(limx0(1+x)1x)=ln(e)=1



We use the fact that aln(b)=ln(ba)



Edit: Based on comments, I added one last step before "ln(e)". This is to showcase that limits have the property that limxx0f(g(x))=f(limxx0g(x)) provided that limxx0g(x)=L,LR and that f is continuous at x=L


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