matrix by matrix in R markdown

Three minor corrections should be sufficient to make this work for both, HTML and PDF output:

1. remove the backslash before the closing bracket in \right\)
2. delete the empty line in the middle
3. specify the column alignment in each array environment, e.g., with \begin{array}{cc}

–

$$
\left(\begin{array}{cc} 
0.8944272 & 0.4472136\\
-0.4472136 & -0.8944272
\end{array}\right)
\left(\begin{array}{cc} 
10 & 0\\ 
0 & 5
\end{array}\right)
$$