Let $ \mathsf{LHS} = \lfloor \lceil x \rceil \rfloor $ and $ \mathsf{RHS} = \lceil x \rceil $.

Let us call $ n = \lceil x \rceil $.

Case 1: $ n $ is even, i.e., there exists a $ k \in \mathbb{Z} $ such that $ n = 2 k $.

I’m not sure how to go on or if I’m setting this up right.

  • $\begingroup$ What is ⎤? Floor? Ceil? $\endgroup$ – Joao Nov 14 '14 at 6:59
  • $\begingroup$ You have to show that, if $n=\lceil x\rceil$, then $\lfloor n\rfloor=n$? If $n$ is the floor of some number then $n$ is its own ceiling? If $n$ is in the range of the floor function, then $n$ is a fixed point of the ceiling function? It would help a lot if I knew (a) what is the range of the floor function, and (b) what are the fixed points of the ceiling function. Beats me. You have any ideas? $\endgroup$ – bof Mar 1 '15 at 8:30
  • $\begingroup$ This question seems a bit simple and should probably be considered off topic or simple. Ceiling returns an integer. Floor only changes a number when it is not an integer. This is really a question of data types. Ceiling changes a number from R -> N. And then floor only does something when changing R -> N. It's a data type converter function. If it's the right data type then casting is literally redundant. The question is nice but I think it's one that CRUDE would say shouldn't be here, sadly. $\endgroup$ – The Great Duck Mar 4 '16 at 5:08

$\lceil x\rceil$ is an integer, and if $n$ is an integer then $\lfloor n\rfloor=n$.


First notice that $ \left \lfloor{n}\right \rfloor = n$ for all integers $ n$. And $ \lceil x \rceil $ is an integer


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