[3−4−12]\left[\begin{array}{rr}3 & -4 \\-1 & 2\end{array}\right][3−1−42]
12[3−1−42]\frac{1}{2}\left[\begin{array}{rr}3 & -1 \\-4 & 2\end{array}\right]21[3−4−12]
12[3−4−12]\frac{1}{2}\left[\begin{array}{rr}3 & -4 \\-1 & 2\end{array}\right]21[3−1−42]
−12[3−4−12]-\frac{1}{2}\left[\begin{array}{rr}3 & -4 \\-1 & 2\end{array}\right]−21[3−1−42]