Determinant of $$$\left[\begin{array}{cc}6 & 1\\9 & -1\end{array}\right]$$$

Calculate $$$\left|\begin{array}{cc}6 & 1\\9 & -1\end{array}\right|$$$.

The determinant of a 2x2 matrix is $$$\left|\begin{array}{cc}a & b\\c & d\end{array}\right| = a d - b c$$$.

$$$\left|\begin{array}{cc}6 & 1\\9 & -1\end{array}\right| = \left(6\right)\cdot \left(-1\right) - \left(1\right)\cdot \left(9\right) = -15$$$

$$$\left|\begin{array}{cc}6 & 1\\9 & -1\end{array}\right| = -15$$$A