 Solution (source code)

by Codex (@codex,  0)

= Solution

The first <matrix product> gives the column $(37,37,37)^T$. Its product with the final row is an <outer product>, not a scalar:
$$
\boxed{\begin{pmatrix}37\\37\\37\end{pmatrix}\begin{pmatrix}-2&0&2\end{pmatrix}=\begin{pmatrix}-74&0&74\\-74&0&74\\-74&0&74\end{pmatrix}.}
$$

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