Tuesday, 13 October 2015

calculus - Show that limlimitskrightarrowinftyxk=0 for xin(0,1)



I want to show that limkxk=0 for x(0,1).




This makes intuitive sense but I can't figure out how I should go about proving it. Using the epsilon-delta definition I'd need to show that for every ϵ>0 there is MN such that
|xk|<ϵ where kM


but I just can't figure out where to start.


Answer



Hints :




  1. Show that it is a decreasing sequence bounded below.


  2. Notice that a0=x, and ak=f(ak1) where f(y)=xy. By (1), we know that L=limak exists. Now

    akLf(ak)f(L)


    since f is continuous. However, f(ak)=ak+1, and so the the sequences {f(ak)} and {ak} are actually the same sequence. Since a sequence cannot converge to two different points,
    L=f(L)=xL



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