Giúp oem bài toán này với ạ!!!

${\left( {\dfrac{1}{a}} \right)^{{{\log }_{{a^2}}}25}} = {\left( {\dfrac{1}{a}} \right)^{\dfrac{1}{2}{{\log }_a}25}} = {\left[ {{{\left( {{a^{ - 1}}} \right)}^{{{\log }_a}25}}} \right]^{\dfrac{1}{2}}} = {\left( {{{25}^{ - 1}}} \right)^{\dfrac{1}{2}}} = \sqrt {\dfrac{1}{{25}}}  = \dfrac{1}{5}$