[tex]\bf ~~~~~~~~~~~~\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}}
\\\\
-------------------------------\\\\
(r^3)^{-2}\implies r^{3\cdot -2}\implies r^{-6}\implies \cfrac{1}{r^6}[/tex]
