9.
阅读材料:对于任何数,我们规定符号\(\left| \begin{matrix} {a} & {b} \\ {c} & {d} \\\end{matrix} \right|\)的意义是\(\left| \begin{matrix} {a} & {b} \\ {c} & {d} \\\end{matrix} \right|=ad{-}bc\).
例如:\(\left| \begin{matrix} {1} & {2} \\ {3} & {4} \\\end{matrix} \right|=1\times 4{-}2\times 3={-}2\)
\((1)\)按照这个规定,请你计算\(\left| \begin{matrix} {2} & {6} \\ {-2} & {4} \\\end{matrix} \right|\)的值.
\((2)\)按照这个规定,请你计算当\({ }\!\!|\!\!{ }x+\dfrac{1}{2}|+{{(y{-}2)}^{2}}=0\)时,
求:\(\left| \begin{matrix} 2{{x}^{2}}{-}y & {{x}^{2}}{-}y \\ 2 & {-}1 \\\end{matrix} \right|\)的值.