[tex]\bf ~\hspace{7em}\textit{negative exponents}
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a^{-n} \implies \cfrac{1}{a^n}
~\hspace{4.5em}
a^n\implies \cfrac{1}{a^{-n}}
~\hspace{4.5em}
\cfrac{a^n}{a^m}\implies a^na^{-m}\implies a^{n-m}
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\left( \cfrac{8\cdot 4\cdot 2}{8\cdot 7} \right)^2\times \left( \cfrac{8^0}{7^{-3}} \right)^3\times 7^{-9}\implies \left( \cfrac{8\cdot 8}{8\cdot 7} \right)^2\times \left( \cfrac{1\cdot 7^3}{1} \right)^3\times \cfrac{1}{7^9}[/tex]
[tex]\bf \left( \cfrac{8}{8}\cdot \cfrac{8}{7} \right)^2\times (7^3)^3\times \cfrac{1}{7^9}\implies \left( \cfrac{8}{7} \right)^2\times 7^{3\cdot 3}\times \cfrac{1}{7^9}\implies \cfrac{8^2}{7^2}\times \cfrac{7^9}{7^9}
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\cfrac{8^2}{7^2}\implies \cfrac{64}{49}[/tex]
