\(\begin{array}{l}
a)|x - 3| = |5| + | - 7|\\
\Leftrightarrow \left| {x - 3} \right| = 5 + 7\\
\Leftrightarrow \left| {x - 3} \right| = 12\\
\Leftrightarrow \left[ \begin{array}{l}
x - 3 = 12\\
x - 3 = - 12
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = 15\\
x = - 9
\end{array} \right.\\
b)4 - \left( {7 - x} \right) = x - \left( {13 - 4} \right)\\
\Leftrightarrow 4 - 7 + x = x - 9\\
\Leftrightarrow - 3 = - 9
\end{array}\)
=>pt vô nghiệm
