Here's the question you clicked on:
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Why does the addition sign change in 9^-(n+2) when you convert it to 1/9^(n-2)?
there is now change \[9^{-(n +2)} = \frac{1}{9^{n + 2}}\] for a proof \[\frac{1}{9^n} \times \frac{1}{9^2} = \frac{1}{9^{(n + 2)}} = 9^{-(n + 2)}\]
so what is happening in this step? http://tutorial.math.lamar.edu/Classes/CalcII/Series_Special_files/eq0020MP.gif
oh. wait i think i get it. nvm