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1. The problem statement, all variables and given/known data

[itex]f: \mathbb{R} \rightarrow \mathbb{Q} [/itex],

show that there is a [itex] q \in \mathbb{Q}[/itex] st. [itex]f^{-1}(q)[/itex] is infinite set in [itex] \mathbb{R}[/itex].

2. Relevant equations

3. The attempt at a solution

how can we show that is true?

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# Homework Help: Infinite set

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