Wednesday

August 20, 2014

August 20, 2014

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

- mathmatics( sequence and series) -
**tchrwill**, Wednesday, November 25, 2009 at 2:02pmThe 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 9:09pmThis same question came up several days ago

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

**Related Questions**

Functions 11: Series and Sequence 2 - The sum of the first two terms of a ...

Math - The first two terms in a geometric series is 12. The sum of the first ...

math - The sum of the first four terms of a G.P.is 30 and that of the last four ...

Math - the sum of the first n terms of an arithmetic series is -51. the series ...

math - thinking/inquiry/problem solving: a formula for the sum of the first n ...

Maths - Gemometric Progression - The sum of the first n terms of a series in n^3...

Further mathematics - An exponential sequence (GP)of positive terms and a linear...

Further mathematics - An exponential sequence of positive terms and a linear ...

Geometric - 1) The sum of last three terms of GP having n terms is 1024 time the...

Algebra II - The first 3 terms in a geometric sequence are 1.1, 1.65, and 2.475...