|x-3|=\left\{\begin{array}{r1}
x-3, & x-3\geq 0\\
-(x-3), & x-3<0
\end{array}
\right.=\left\{\begin{array}{r1}
x-3, & x\geq 3\\
-x+3, & x<3
\end{array}
\right.