\[\boxed{\text{489\ (489).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ \sqrt{( - a)^{2}} = \sqrt{a^{2}} = |a|\]
\[\textbf{б)}\ \sqrt{( - a)^{2}( - b)^{4}} = \sqrt{a^{2} \cdot \left( b^{2} \right)^{2}} =\]
\[= \sqrt{a^{2}} \cdot \sqrt{\left( b^{2} \right)^{2}} = |a| \cdot \left| b^{2} \right|\]
\[b^{2} \geq 0\ при\ любом\ b:\]
\[|a| \cdot \left| b^{2} \right| = |a| \cdot b^{2}\text{.\ }\]