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Find the determinant of the matrix $A = \begin{pmatrix} 7 & -6 \\ -1 & -8 \end{pmatrix}$.
Substitute the values. Hint: The determinant of $\begin{pmatrix} a & b \\ c & d \end{pmatrix}$ is $\operatorname{det} A = ad - bc$.
$\operatorname{det} A = \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{A1}}\hspace{54px}}~} \times \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{A2}}\hspace{54px}}~} - \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{A3}}\hspace{54px}}~} \times \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{A4}}\hspace{54px}}~}$ $\operatorname{det} A = [7] \times [-8] - [-6] \times [-1]$
Therefore,
$\operatorname{det} A = \class{inputBox step2}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{B1}}\hspace{54px}}~} - \class{inputBox step2}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{B2}}\hspace{54px}}~} = \class{inputBox step2}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{BR}}\hspace{54px}}~}$ $\operatorname{det} A = [-56] - [6] = [-62]$