HI!

=3^-2= Positif
=-3^-2=Positif
In your example: (-3)^(-2/3) returns #NUM!, because (-2/3)< that 1
-3^-(number<1) it's impossible.
in your other example: ((-3)^(-2))^(1/3) is ok.because ((-3)^(-2))=Positif
Try
=3^(-2/3)

Starwing