\[\boxed{\text{4.\ 351}}\]
\[\textbf{а)}\ |a| = a\]
\[a - любое\ число.\ \]
\[\textbf{б)}\ |a| = - a\]
\[a < 0.\]
\[\textbf{в)}\ | - a| = a\]
\[a \geq 0.\]
\[\textbf{г)}\ | - a| = - a\]
\[a < 0.\]
\[\textbf{д)}\ a = - a\]
\[a = 0.\ \]
\[\textbf{е)}\ |a| + a = 0\]
\[a \leq 0.\]
\[\textbf{ж)}\ |a| + a = 2a\]
\[a > 0.\]
\[\textbf{з)}\ a - |a| = 2a\]
\[a < 0.\]