A Continued Reciprocal Function

Problem

A function on [1,+)[1, +\infty) is defined by

f(x)={1,1x<2,f(x1)1+f(x1),x2.f(x) = \begin{cases} 1, & 1 \leqslant x < 2, \\[2pt] \dfrac{f(x-1)}{1 + f(x-1)}, & x \geqslant 2. \end{cases}

Determine, with proof, which of the following are true:

1. f(2024)=12024f(2024) = \dfrac{1}{2024}; 2. for x>1x > 1, 1xf(x)<1x1\dfrac{1}{x} \leqslant f(x) < \dfrac{1}{x-1}; 3. if f(x)kx+1f(x) \leqslant \dfrac{k}{x+1} for all xx, then the minimum value of kk is 22; 4. if f(x)axf(x) \geqslant a^x (with a>0a > 0, a1a \neq 1) for all xx, then the maximum value of aa is 933\dfrac{\sqrt[3]{9}}{3}.

Answer

Solution

Difficulty7/10
Topicsfunctions, Monotonicity, Recursion, sequences, Logarithms, inequality

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