[tex]\dfrac{2}{3}[(5+3)^{-3}]=\dfrac{2}{3}(8)^{-3}\\\\\text{use}\ a^{-n}=\dfrac{1}{a^n}\\\\=\dfrac{2}{3}\cdot\dfrac{1}{8^3}=\dfrac{2}{3\cdot512}=\dfrac{1}{3\cdot256}=\dfrac{1}{768}[/tex]
