Posted by **achyut** on Wednesday, November 25, 2009 at 11:00am.

The sum of the first four terms of a G.P.is 30 and that of the last four terms is 960. If the first and the last term of the G.P. are 2 and 512 respectively, find the the common ratio

- mathmatics( sequence and series) -
**tchrwill**, Wednesday, November 25, 2009 at 2:02pm
The sum of the first four terms of a G.P.is 30 and that of the last four terms is 960. If the first and the last term of the G.P. are 2 and 512 respectively, find the the common ratio.

The sum of n terms is given by S = a(r^n - 1)/(r - 1) where a = the first term, n = the number of terms and r = the common ratio.

Therefore, the sum of the first 4 terms, as defined, is S = 2(r^4 - 1)/(r - 1) which results in r^4 - 15r = -14.

At first inspection, r = 2.

- mathmatics( sequence and series) -
**Reiny**, Wednesday, November 25, 2009 at 9:09pm
This same question came up several days ago

http://www.jiskha.com/display.cgi?id=1258559554

- mathmatics( sequence and series) -
**Anonymous**, Friday, August 19, 2016 at 2:44pm
the last term is 512 and common ratio is 2 then its 5th term

## Answer This Question

## Related Questions

- math - The sum of the first four terms of a G.P.is 30 and that of the last four ...
- MATH!! - ~Determine whether each sequence is arithmetic or geometric fund the ...
- Functions 11: Series and Sequence 2 - The sum of the first two terms of a ...
- Math - the sum of the first n terms of an arithmetic series is -51. the series ...
- Geometric - 1) The sum of last three terms of GP having n terms is 1024 time the...
- Maths - Gemometric Progression - The sum of the first n terms of a series in n^3...
- math - in an arithmetic sequence the common difference is equal to 2.the first ...
- math - The first and second terms of an exponential sequence (G.P) are ...
- Further mathematics - An exponential sequence (GP)of positive terms and a linear...
- Algebra II - The first 3 terms in a geometric sequence are 1.1, 1.65, and 2.475...

More Related Questions