Algebra and Trigonometry 10th Edition

The determinant of a $2 \times 2$ matrix can be computed by using the formula $det =ps-qr$ where $det =\begin{bmatrix}p & q \\r & s\end{bmatrix}$ Considering the left side, we have: $det=wcx-cwx=wcx-wcx=0$ Now, considering the right side we have $det=0$