Bear in mind that, (-9) and -9 are very different mammals, we're assuming, you meant (-9)⁻¹.
[tex]\bf \left.\qquad \qquad \right.\textit{negative exponents}\\\\
a^{-{ n}} \implies \cfrac{1}{a^{ n}}
\qquad \qquad
\cfrac{1}{a^{ n}}\implies a^{-{ n}}
\qquad \qquad
a^{{{ n}}}\implies \cfrac{1}{a^{-{{ n}}}}
\\\\
-------------------------------\\\\
(-9)^{-1}\implies \cfrac{1}{-9}\implies -\cfrac{1}{9}[/tex]
