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18 votes
3, -9, 27, -81,... Explicit Formula an = -9 . 3n-1 an = 3 . -3n-1an = -9 . 27n-1 an = 3 - 3 ( n- 1 )

User NickMcB
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1 Answer

25 votes
25 votes

To find the explicit form we have find r so we divide the second term by the first one so:


r=-(9)/(3)=-3

Now we know that the formula is:


\begin{gathered} a_n=a_0r^(n-1) \\ a_n=3(-3)^(n-1) \end{gathered}

So the answer is option D

User Blink
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