Floor of Number plus Integer

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Theorem

$\forall n \in \Z: \floor x + n = \floor {x + n}$

where $\floor x$ denotes the floor of $x$.


Proof

\(\ds \floor {x + n}\) \(\le\) \(\, \ds x + n \, \) \(\, \ds < \, \) \(\ds \floor {x + n} + 1\) Definition of Floor Function
\(\ds \leadsto \ \ \) \(\ds \floor {x + n} - n\) \(\le\) \(\, \ds x \, \) \(\, \ds < \, \) \(\ds \floor {x + n} - n + 1\)
\(\ds \leadsto \ \ \) \(\ds \floor x\) \(=\) \(\ds \floor {x + n} - n\) Definition of Floor Function
\(\ds \leadsto \ \ \) \(\ds \floor {x + n}\) \(=\) \(\ds \floor x + n\) adding $n$ to both sides

$\blacksquare$


Also see