Salutare!
Formula: [tex]\boxed{(\frac{x}{y} )^{-m} = (\frac{y}{x})^m}[/tex]
Exemple:
a) [tex]2^{-3} =( \frac{1}{2})^3 = \frac{1}{8}[/tex]
b) [tex](\frac{3}{4})^{-2} =( \frac{4}{3} )^2 = \frac{16}{9}[/tex]
c) [tex]0,5^{-3} = (\frac{1}{2})^{-3} = (\frac{2}{1} )^3 = 2^3 = 8[/tex]