Logarithmic & Exponential Functions

Exponentials and logarithms

$y = a^x$ ($a > 0$) is an exponential function; its inverse is the logarithm $x = \log_a y$. Thus

$$y = a^x \iff x = \log_a y$$

The natural exponential uses $e \approx 2.718$; its inverse is $\ln x = \log_e x$.