Look at the picture.
[tex]|a|=\left\{\begin{array}{ccc}a&for&a\geq0\\-a&for&a < 0\end{array}\right\\\\|9-8x|=\left\{\begin{array}{ccc}9-8x&for&x\in\left(-\infty,\ \dfrac{9}{8}\right]\\-(9-8x)&for&x\in\left(\dfrac{9}{8},\ \infty\right)\end{array}\right[/tex]
