测试 LaTeX

This is an array.

\begin{array}{cc}
a & b \\
c & d
\end{array}

In equation \eqref{eq:sample}, we find the value of an interesting integral:
\begin{equation}
\int_0^\infty \frac{x^3}{e^x-1}\,dx = \frac{\pi^4}{15} \label{eq:sample}
\end{equation}