[tex](5\sqrt 2 )^{-2} = \dfrac{1}{(5\sqrt{2})^2} = \dfrac{1}{5^2\cdot \sqrt2^2} = \dfrac{1}{25\cdot 2} = \dfrac{1}{50} \\ \\ \\ (5\sqrt2)^{-2} = \Big[(5 \sqrt2)^2\Big]^{-1}= \Big(5^2\cdot \sqrt2^2\Big)^{-1} = (25\cdot 2)^{-1}= 50^{-1} = \dfrac{1}{50} [/tex]
