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October 25, 2014

October 25, 2014

Posted by **Chelsey** on Saturday, November 17, 2007 at 8:07pm.

I had a_n=-12(3)^(n-1) but that is not a choice on the multiple answers

they have = -12(1/3)^(n-1)

= 12(-1/3)^(n-1)

= -12(-1/3)^(-n+1)

= -12 (-1/3)^(n-1)

- Algebra 2 -
**Michael**, Saturday, November 17, 2007 at 8:15pmWe're dividing by -3, so r (the common ratio) is -1/3. The -1/3 is the number by which we're multiplying the previous term. The common ratio always has to be the number that is MULTIPLIED to get the next term. In this example, (-12)(-1/3) = 4 and 4(-1/3) = -4/3.

The formula for calculating the nth term in a geometric sequence is...

tn = t1 . r^(n - 1)

the nth term = the first term * the common ratio^(n-1)

Just plug in our numbers. The first term is 12, and the common ratio is -1/3.

tn = -12(-1/3)^(n-1)

That's the last option above.

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