# Inverse hyperbolic sine function

The inverse hyperbolic sine function, denoted $\sinh^{-1}$, is defined in the following equivalent ways:
1. It is the inverse function to the hyperbolic sine function, i.e., $\sinh^{-1}x$ is defined as the unique real number $y$ such that $\sinh y = x$.
$\sinh^{-1} x := \ln|x + \sqrt{x^2 + 1}|$