Is $n\lceil x \rceil = \lceil nx \rceil$, for all integers $n$ and real numbers $x$? If not, are there some similar (or less general) rules available? If yes, can this somehow be generalized?
Simple question about the ceiling function
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0You'll find some inequalities (for $\lfloor \cdot \rfloor$) [here](http://math.stackexchange.com/q/60465/19341). The answer uses the Hermite's identity, mentioned by Dejan. – 2012-04-04
2 Answers
No, for example $2\lceil \frac 14 \rceil \ne \lceil 2\cdot \frac 14 \rceil$
No, $n\lceil x\rceil$ is not in general equal to $\lceil nx\rceil$, as easy examples will show you; for instance, just take $n=2$ and $x=1/2$, so that $n\lceil x\rceil=2$ and $\lceil nx\rceil=1$.
To see what happens in general, suppose that $n$ is positive and that $\lceil x\rceil=m$; this amounts to saying that $x=m-1+\alpha$, where $0<\alpha\le 1$. Then $nx=(m-1)n+n\alpha$, so $\lceil nx\rceil=\lceil (m-1)n+n\alpha\rceil=(m-1)n+\lceil n\alpha\rceil\;.$
Since $0<\alpha\le 1$, there must be a unique integer $k$ such that $0