\left(\begin{array}{rrr}
0 & 2 & -1 \\
1 & 1 & 10
\end{array}\right)
\left(\begin{array}{rrr}
1 & 5 & 8 \\
-91 & 45 & 100
\end{array}\right)
\left(\begin{array}{rr}
1 & 2 \\
3 & 4
\end{array}\right)
\left(\begin{array}{rr}
1 & 2 \\
3 & 4
\end{array}\right)
\left(\begin{array}{rrr}
0 & 2 & -1 \\
1 & 1 & 10
\end{array}\right)
\left(\begin{array}{rrr}
1 & 0 & \frac{21}{2} \\
0 & 1 & -\frac{1}{2}
\end{array}\right)
\left(\begin{array}{rrrr}
1 & 0 & 0 & 0 \\
0 & 1 & 0 & 0 \\
0 & 0 & 1 & 0 \\
0 & 0 & 0 & 1
\end{array}\right)
\left(\begin{array}{rr}
1 & 2 \\
3 & 4
\end{array}\right)
\left(\begin{array}{rrr}
0 & 2 & -1 \\
1 & 1 & 10
\end{array}\right)
\left(\begin{array}{rrr}
0 & 2 & -1 \\
1 & 1 & 10
\end{array}\right)
\left(\begin{array}{rr}
0 & 1 \\
2 & 1 \\
-1 & 10
\end{array}\right)
i.
ii.
\left(\begin{array}{rr}
1 & 10 \\
81 & 723 \\
-1 & 766
\end{array}\right)
\left(\begin{array}{rr}
1 & 10 \\
81 & 723 \\
-1 & 766
\end{array}\right)
iii.
\left(\begin{array}{rr}
10 & -910 \\
50 & 450 \\
80 & 1000
\end{array}\right)
-2
\left(\begin{array}{rr}
1 & 2 \\
2 & 4
\end{array}\right)
\left(\begin{array}{rr}
-2 & \frac{3}{2} \\
1 & -\frac{1}{2}
\end{array}\right)
\left(\begin{array}{rr}
\cos\left(\theta\right)^{2} - \sin\left(\theta\right)^{2} & 2 \, \cos\left(\theta\right) \sin\left(\theta\right) \\
-2 \, \cos\left(\theta\right) \sin\left(\theta\right) & \cos\left(\theta\right)^{2} - \sin\left(\theta\right)^{2}
\end{array}\right)
\left(\begin{array}{rr}
1 & -1 \\
1 & 1
\end{array}\right)
\left( a, b \right) \ {\mapsto} \ \left(a - b,\,a + b\right)
We're Correct
\left(\begin{array}{rr}
1 & 1 \\
-1 & 1
\end{array}\right)
\left(\begin{array}{rr}
2 & -5 \\
0 & 0 \\
1 & 4 \\
0 & 1
\end{array}\right)
\left( x_{1}, x_{2} \right) \ {\mapsto} \ \left(2 \, x_{1} - 5 \, x_{2},\,0,\,x_{1} + 4 \, x_{2},\,x_{2}\right)
\left(\begin{array}{rr}
2 & -5 \\
0 & 0 \\
1 & 4 \\
0 & 1
\end{array}\right)