Saturday 28 November 2015

calculus - fractional part of the square of natural number



How can if prove that the sequence :$$a_n\:=\left\{\sqrt{n}\right\}\left(fractional\:part\:of\:\sqrt{n}\right)\:=\:\:\sqrt{n}\:-\:\left[\sqrt{n}\right]$$
is bounded from above by 1?
So far i try induction but its nothing that the assumption can help me for the "step" of the induction so i kind of stuck here.
tnx!




*($[x]$ - the floor function of x)


Answer



The fractional part of a number is, by definition, between $0$ and $1$. This is because $[x]$, the integer part of $x$, is defined as




The largest integer $n\in\mathbb Z$ such that $n



Therefore, if $x-[x] > 1$, then $[x]+1$ is:





  • smaller than $x$ (because $x-[x]>1$ can be rearanged to $x>[x]+1$)

  • larger than $[x]$ (by definition, it is larger by $1$.



meaning that $[x]$ is not the largest integer satisfying $n

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