For what value of $k$ is $\begin{bmatrix} k & 4 \\ -2 & 8 \end{bmatrix}$ a singular matrix?

Explanation

1. 01

   A matrix is singular when its determinant is 0, and then it has no inverse.

2. 02

   $8k - (4)(-2) = 8k + 8 = 0$ gives $k = -1$.