\[\boxed{\mathbf{517\ (517).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ y = \sqrt{x^{2}} - 2x,\ \ x \geq 0\]
\[y = |x| - 2x\]
\[y = x - 2x\]
\[y = - x\]
\[2)\ y = \sqrt{- x} \cdot \sqrt{- x}\]
\[y = \sqrt{x^{2}}\]
\[y = |x|\]
\[y = \left\{ \begin{matrix} x,\ \ x \geq 0 \\ - x,\ \ x < 0 \\ \end{matrix} \right.\ \ \]
\[\boxed{\mathbf{51}\mathbf{7}\text{.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[1)\ |a| = a\]
\[если\ a \geq 0.\]
\[2)\ |a| = - a\text{\ \ }\]
\[если\ a < 0.\]
\[3)\ |a| = | - a|\text{\ \ }\]
\[если\ a - любое\ число.\]
\[4)\ |a| = - |a|\text{\ \ }\]
\[если\ a = 0.\ \]