Here is my try
Let $\Gamma$ be an $2\times 2$ Hermitian matrix,\\
\begin{displaymath}
\begin{equation}
$\Gamma$ = $\begin{bmatrix} $\gamma 1$ & $\gamma 2$\\ $\gamma 3$ &$\gamma 4$
\end{bmatrix}
\end{equation}
\end{displaymath}
equationsmatrices
Best Answer
let me convert my comment to an answer:
\begin{equation} ... \end{equation}
inside\begin{displaymath} ... \end{displaymath}
,$
inside equation is not allowed (it is intend for use for math expression in text)where is, as noted Mico in his comment below,
\[ ... \]
entirely equivalent to\begin{displaymath} ... \end{displaymath}
.or an alternative to the leandriis answer, as suggested Bernard in his comment below:
which gives:
and one more (final) alternative :-), as suggested barbara beeton in her comment below:
which gives