Sum of a number of terms in g.p., Mathematics

Assignment Help:

We know that the terms in G.P. are:

a, ar, ar2, ar3, ar4, ................, arn-1

Let s be the sum of these terms, then

s = a + ar + ar2 + ar3 + ar4 + ................+ arn-1

                            or

s

 = 1058_GP.png

This is obtained as follows:

We know that

s = a + ar + ar2 + ar3 + ar4 +.............+ arn - 1                                            ......(1)

Multiplying this with "r" throughout, we have

r.s     = r.a + r.ar + r.ar2 + r.ar3 + r.ar4 +........+ r.arn-1 

         = ar + ar2 + ar3 + ar4 + ar5 +.......+ arn                                             ......(2)

Subtracting (1) from (2), we have

r.s - s = (ar - a) + (ar2 - ar) + (ar3 - ar2) +.......+ (arn - arn-1)

After canceling the terms equal in magnitude but opposite in sign, we are left with

s(r - 1) = arn - a
s(r - 1) = a(rn - 1)
 or s    = 427_GP1.png

By changing the signs in the numerator and the denominator we can also write the above equation as

 s  = 1058_GP.png

What happens to the above formula if the value of n is very large. The above formula can be written as

s

916_GP2.png

As the value of n approaches infinity (very large) the expression  2050_GP3.png becomes smaller to that extent where we ignore it. In this case the nth term is given as

Tn

= 1193_GP4.png

Now we look at a couple of examples.

Example

Find the sum of the series which is given below to 13 terms.

                   81, 54, 36, .............

The first term 'a' = 81 and the common ratio is obtained from the ratio of 54 and 81 or 36 and 54. It is 54/81 = 2/3. Now we employ the formula given above to calculate the sum of series to 13 terms.

s =   

1772_GP5.png

       = 241.78

The same series if considered as an infinite series, the sum of n terms would be

T = 491_GP6.png

= 243

Related Discussions:- Sum of a number of terms in g.p.

How many inches is the smaller dimension of the decreased, A photographer d...

A photographer decides to decrease a picture she took in sequence to fit it within a certain frame. She requires the picture to be one-third of the area of the original. If the ori

Limits at infinity, Limits At Infinity, Part I : In the earlier section w...

Limits At Infinity, Part I : In the earlier section we saw limits which were infinity and now it's time to take a look at limits at infinity.  Through limits at infinity we mean

Project, report on shares and dividend using newspaper

report on shares and dividend using newspaper

Derive the hicksian demand function using indirect utility , (a) Derive the...

(a) Derive the Marshalian demand functions and the indirect utility function for the following utility function: u(x1, x2, x3) = x1 1/6 x2 1/6 x3 1/6    x1≥ 0, x2≥0,x3≥ 0

Math project , Topic 1: Statistical Studies Find two different news storie...

Topic 1: Statistical Studies Find two different news stories in a mainstream media source (CNN, FoxNews, Newsweek, etc.), that cite data from a recognized poling agency. Locate th

Variation and proportion, i am not getting what miss has taught us please w...

i am not getting what miss has taught us please will you will help me in my studies

Daily Math, Six times as many people voted in the 2012 election as in the 2...

Six times as many people voted in the 2012 election as in the 2008 election.If 162 people voted in 2008,how many people voted in both elections?

Differential equation, Verify Liouville''''s formula for y "-y" - y'''' + y...

Verify Liouville''''s formula for y "-y" - y'''' + y = 0 in (0, 1)

What is the objective of lipids metabolism, What is the objective of lipids...

What is the objective of lipids metabolism ? After studying this unit, you will be able to: 1. explain how fatty acids are oxidized for the production of energy, 2. describe

What is a percentage, Q. What is a percentage? Ans. Percent  mean...

Q. What is a percentage? Ans. Percent  means "per hundred", or "out of 100". A percentage can be written as a ratio, or fraction, where the denominator (bottom) is 100.

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd