\[\boxed{\text{225\ (225).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ |x| = | - x|;\ \ \ так\ как:\ \]
\[| - x| = | - 1 \cdot x| = | - 1| \cdot |x| = |x|.\]
\[\textbf{б)}\ |x - y| = |y - x|;\ \ \ \ \ так\ как:\ \]
\[|x - y| = \left| - 1 \cdot (y - x) \right| =\]
\[= | - 1| \cdot |y - x| = |y - x|.\]
\[\textbf{в)}\ |2c| = 2|c|;\ \ \ так\ как:\ \]
\[|2c| = |2| \cdot |c| = 2 \cdot |c|.\]