Question

How do you simplify `(mn^(-4/5))^(-5/7)`?

Answer 1

You can use the fact that `(a^m)^n=a^(m*n)` and get:
`m^(1*(-5/7))n^((-4/5)*(-5/7))=m^(-5/7)n^(4/7)`
If you want you can change them into roots using `a^(m/n)=rootn(a^m)` (and the fact that `a^-m=1/a^m`).