## Precalculus (10th Edition)

We know that for a matrix $\left[\begin{array}{rr} a & b \\ c &d \\ \end{array} \right]$ the determinant $D$ is given by the formula $D=ad-bc.$ We also know that if $D=0$, then the matrix is singular. The given matrix has $D=(4\cdot2)-[(-8)\cdot(-1)]\\ D=8-8\\ D=0$ The square matrix has a determinant of zero therefore it is singular.