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Finites series product sum question

thepikminman · 2016-04-02 23:39:36

Hi, I'm struggling with this question: Calculate the sum of the first 39 terms of the sequence: 4/9, 2/3, 1, 3/2, 9/4, 27/8, 81/16, .... I can see that each term is multiplied the 3/2 and I got to the equation: (3^(n-3))x(2^(3-n)) and this works to get any nth term, but I am unsure how to get the sum. Any help?

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03-04-2016 12:39am

#1

thepikminman

Registered Users Posts: 178 ✭✭

Join Date: February 2012

Posts: 141

Hi,

I'm struggling with this question:

Calculate the sum of the first 39 terms of the sequence:
4/9, 2/3, 1, 3/2, 9/4, 27/8, 81/16, ....

I can see that each term is multiplied the 3/2 and I got to the equation:
(3^(n-3))x(2^(3-n)) and this works to get any nth term, but I am unsure how to get the sum. Any help?

0

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#2 03-04-2016 8:27pm
TheBody

Registered Users Posts: 5,619 ✭✭✭

Join Date: January 2011

Posts: 5484

It's just a geometric series.

Have a look at this and see if you can figure it out.

http://www.regentsprep.org/regents/math/algtrig/atp2/geoseq.htm

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#3 03-04-2016 11:12pm
thepikminman

Registered Users Posts: 178 ✭✭

Join Date: February 2012

Posts: 141

TheBody wrote: »

It's just a geometric series.

Have a look at this and see if you can figure it out.

http://www.regentsprep.org/regents/math/algtrig/atp2/geoseq.htm

Thank you, perfect!!

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#4 04-04-2016 8:23am
TheBody

Registered Users Posts: 5,619 ✭✭✭

Join Date: January 2011

Posts: 5484

No problem. Glad you got sorted.

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