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Where $n-k\gg1$ and $k\gg\sqrt{n}$ and $A=2$ is a constant.
And $n\rightarrow\infty$.
My thoughts is that $f\left(n\right)\rightarrow 0$ (I have ran some examples in walfram alpha and desmos)
But I am not quite sure how to approach this problem and I would like some help.