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**dhYTvlAv** · 12-27-2007, 03:10 PM

Find the common ratio and the first term in the geometric progressions where the 2nd term is 4 and the 5th term is 108.

I can't for the life of me recall how to do this. Anybody can help me with this?

Can I use the ar^n-1 formula for this question?

**khjhkfggt** · 12-27-2007, 03:28 PM

4 = a*r
108 = a*r^4

a = 4/r
108 = (4/r)(r^4)
r^3 = 27
r = 3

4 = a*3
a = 4/3

right?

**dhYTvlAv** · 12-27-2007, 03:37 PM

Yes that's right. Thanks.

12-27-2007, 03:10 PM	#1
dhYTvlAv Join Date Oct 2005 Posts 519 Senior Member	Math help Find the common ratio and the first term in the geometric progressions where the 2nd term is 4 and the 5th term is 108. I can't for the life of me recall how to do this. Anybody can help me with this? Can I use the ar^n-1 formula for this question? Share Share this post on Digg Del.icio.us Technorati Twitter
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12-27-2007, 03:28 PM	#2
khjhkfggt Join Date Oct 2005 Posts 396 Senior Member	4 = ar 108 = ar^4 a = 4/r 108 = (4/r)(r^4) r^3 = 27 r = 3 4 = a*3 a = 4/3 right? Share Share this post on Digg Del.icio.us Technorati Twitter
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12-27-2007, 03:37 PM	#3
dhYTvlAv Join Date Oct 2005 Posts 519 Senior Member	Yes that's right. Thanks. Share Share this post on Digg Del.icio.us Technorati Twitter
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