解：???$(2)(\frac 54)3=\frac 54×\frac 54×\frac 54=\frac {125}{64}$???
???$ {(\frac 45)}^{-3}=\frac 1{(\frac 45)3}=\frac 1{\frac 45×\frac 45×\frac 45}=\frac {125}{64}$???
所以???$(\frac 54)3={(\frac 45)}^{-3}$???
???$ (3)$???相等，理由如下：
因為???${(\frac ba)}^m=\frac {b^m}{a^m}$???
???$ {(\frac ab)}^{-m}=\frac 1{{(\frac ab)}^m}=\frac 1{\frac {a^m}{b^m}}=\frac {b^m}{a^m}$???
所以???${(\frac ba)}^m={(\frac ab)}^{-m}$???
???$ (4)$???原式???$={(\frac {15}7)}^4×{(\frac 75)}^4={(\frac {15}7×\frac 75)}^4=3^4=81$???
