[Fact] - Wroskian of two functions

The Wroskian of two functions $f(x),g(x)$ is
$\left| \begin{array}{cc}
f(x) & g(x)\\
f'(x) & g'(x)
\end{array} \right| = f(x) \cdot g'(x) - f'(x) \cdot g(x)$.

(From MIT 18.03 lecture 11.)