Question
Prove that the function $\text{f}(\text{x})=\log_{\text{e}}\text{x}$ is increasing on $(0,\infty).$

Answer

Let $\text{x}_1,\text{x}_2\in(0,\infty)$ such that x1 < x2. Then

x1 < x2

Implies that $\log_{\text{e}}\text{x}_1<\log_{\text{e}}\text{x}_2$

Implies that f(x1) < f(x2)

$\therefore$ x1 < x2 Implies that 
$\text{f}(\text{x}_1)<\text{f}(\text{x}_2),\forall\ \text{x}_1,\text{x}_2\in(0,\infty)$

Therefore, f(x) is increasing on $(0,\infty)$

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