Exponential of Real Number is Strictly Positive/Proof 4
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Theorem
Let $x$ be a real number.
Let $\exp$ denote the (real) exponential function.
Then:
- $\forall x \in \R : \exp x > 0$
Proof
This proof assumes the definition of $\exp$ as the inverse mapping of extension of $\ln$, where $\ln$ denotes the natural logarithm.
Recall that the domain of $\ln$ is $\R_{>0}$.
From the definition of inverse mapping, the image of $\exp$ is the domain of $\ln$.
That is, the image of $\exp$ is $\R_{>0}$.
Hence the result.
$\blacksquare$