Problem:
Compute the trace of
$\left(
\begin{array}{ccc}
 -2 & -7 & 0 \\
 -5 & 9 & 5 \\
 3 & -9 & -8 \\
\end{array}
\right)$.
Answer:
\begin{array}{l}
 
\begin{array}{l}
 \text{Find the trace of the matrix:} \\
 \left(
\begin{array}{ccc}
 -2 & -7 & 0 \\
 -5 & 9 & 5 \\
 3 & -9 & -8 \\
\end{array}
\right) \\
\end{array}
 \\
\hline
 
\begin{array}{l}
 \text{Locate }\text{the }\text{elements }\text{on }\text{the }\text{main }\text{diagonal}: \\
 \left(
\begin{array}{ccc}
 -2 & -7 & 0 \\
 -5 & 9 & 5 \\
 3 & -9 & -8 \\
\end{array}
\right) \\
\end{array}
 \\
 
\begin{array}{l}
 \text{Write }\text{out }\text{the }\text{sum }\text{of }\text{the }\text{elements }\text{on }\text{the }\text{main }\text{diagonal}: \\
 -2\, \text{+$\, $}9\, \text{+$\, $}-8 \\
\end{array}
 \\
 
\begin{array}{l}
 -2+9-8=9-(2+8): \\
 9-(2+8) \\
\end{array}
 \\
 
\begin{array}{l}
 2+8=10: \\
 9-10 \\
\end{array}
 \\
 
\begin{array}{l}
 9-10=-1: \\
 \fbox{$
\begin{array}{ll}
 \text{Answer:} &  \\
 \text{} & -1 \\
\end{array}
$} \\
\end{array}
 \\
\end{array}

{'source': 'AMPS', 'file': 'amps/mathematica/linear_algebra/trace_w_steps/3261.txt'}