An Integer Sign Condition

Problem

Let f(x)=ax−mf(x) = ax - m (with m∈N∗m \in \mathbb{N}^*) and g(x)=ln⁡xag(x) = \ln\dfrac{x}{a}. If

f(x)⋅g(x)⩾0for every x∈N∗,f(x)\cdot g(x) \geqslant 0 \qquad \text{for every } x \in \mathbb{N}^*,

find the range of possible values of the real number aa.

Answer

Solution

Difficulty8/10
Topicsfunctions, number theory, Logarithms, inequality, Casework

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