If A = \begin{bmatrix}
A & B \\
C & D
\end{bmatrix}, find \det(A).
Find \begin{vmatrix}
A & B \\
C & D
\end{vmatrix}.
\begin{vmatrix}
\color{red}{A} & \color{purple}{B} \\
\color{blue}{C} & \color{green}{D}
\end{vmatrix} = \color{red}{negParens(A)} \cdot \color{green}{negParens(D)} - \color{blue}{negParens(C)} \cdot \color{purple}{negParens(B)}
\hphantom{\begin{vmatrix}
A & B \\
C & D
\end{vmatrix}} = A * D - negParens(B * C)
\hphantom{\begin{vmatrix}
A & B \\
C & D
\end{vmatrix}} = A * D - B * C