For this case we have that by definition of power properties:
[tex]a ^ {- 1} = \frac {1} {a ^ 1} = \frac {1} {a}[/tex]
We have the following expression:
[tex]r^{-7} + s ^{-12}[/tex]
We can rewrite it as:
[tex]\frac {1} {r ^ 7} + \frac {1} {s ^{ 12}}[/tex]
Finally:
[tex]r ^ {- 7} + s ^ {- 12} = \frac {1} {r ^ 7} + \frac {1} {s ^ {12}}[/tex]
Answer:
Option D
