[tex]\left(\dfrac{2}{\sqrt 8} \right)^3\\\\\\=\left(\dfrac{2}{2\sqrt 2} \right)^3\\\\\\=\left(\dfrac 1{\sqrt 2} \right)^3\\\\\\=\left[\left(\sqrt2 \right)^{-1} \right]^3\\\\\\=\left(\sqrt 2 \right)^{-3}\\\\\\=\left(2^{\tfrac 12} \right)^{-3}\\\\\\=2^{-\tfrac 32}[/tex]
