Answer
$0$
Work Step by Step
The determinant $D$ of a $ 2 \times 2$ matrix can be calculated as:
$D=\left|\begin{array}{ll}
A & B\\C & D \end{array}\right|=AD-BC$
The determinant $D$ of a given $ 2 \times 2$ matrix can be calculated as:
$D=\left|\begin{array}{ll}
x & 4x\\ 2x & 8x \end{array}\right|=(x)(8x)-(2x)(4x)=8x^2-8x^2=0$
