18. Test math extensions E = m c^2

This is inline math: a^2 + b^2 = c^2.

a^2 + b^2 = c^2
\begin{split}a + 1 < b\end{split}
(1)
e^{i\pi} = 1
(2)
e^{ix} = \cos x + i\sin x
n \in \mathbb N
a + 1 < b

Referencing equation (1).