[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}}}}\\\\
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2^n=\cfrac{1}{8}\qquad \boxed{8=2^3}\qquad 2^n=\cfrac{1}{2^3}\implies 2^n=2^{-3}
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\textit{the base is the same, the exponents must also be the same}\quad n=-3[/tex]