Graph of the Exponential Function $y = e^x$

$y = e^x$ is the exponential function with base $e \approx 2.718$; its domain is all real numbers and its range is $y > 0$.

As $x \to -\infty$ it approaches $0$ (the $x$-axis is an asymptote) and grows rapidly as $x$ increases. It is its own derivative — a defining property — and it is the inverse of the natural logarithm $\ln x$.