In this mini-leskid, we target finding the sum of a GP. Let us learn to discover the sum of n regards to a GP, sum of infinite GP, the sum of GP formula, the amount of terms in GP, the sum of finite GP, the amount of boundless terms in GP, the sum of geometric progression

Clara conserves a couple of dollars eexceptionally week in a details fashion.In week 1 she deposits $2. In week 2 -$4, in week 3 - $8, in week 4 - $16, and also so on. How much will certainly she have actually at the finish of 6 weeks in her piggy bank?


A series of numbers derived by multiplying or separating each preceding term, such that tbelow is a common proportion in between the terms (that is not equal to 0) is the geometric progression and the amount of all these terms formed so is the sum of the geometric development.

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Here, the amount built up eextremely week has actually a consistent proportion of $2 and the initial worth is $2.

The amount deposited eextremely week would be $2,$4,$8,$16,$32,$64.

So, at the end of 6 weeks she will certainly have $2+$4 + $8+ $16+ $32 +$64 + $126gathered in her piggy financial institution.

We deserve to discover the very same utilizing the formula of the sum of GP of "n" terms. Let's learn to calculate it now.

Leskid Plan

1.What Is the Sum of a Geometric Progression?
2.Important Notes on Sum of a GP
3.Solved Instances on Sum of a GP
4.Challenging Questions on Sum of a GP
5.Interenergetic Questions on Sum of a GP

What Is the Sum of Geometric Progression?

Let's comment on how to sum an arbitrary GP. Consider the sum of the initially n terms of a GP with first term (a) and prevalent ratio (r).

Sum of the geometric development is:

Multiply both sides by r, and also compose the terms through the very same power of r below each other, as presented below:

<eginalignS & = a + ar + ar^2 + ... + ar^n - 1\\rS &= ar + ar^2+ ... + ar^n - 1+ ar^nendalign>

Now, subtract the initially relation from the second relation:

<(r - 1)S = ar^n - a>

Hence the sum of GP formula if r>1 is offered by:

(S_n = dfraca(r^n-1)r - 1, r eq 1)

Hence the amount of GP formula if r(S_n = dfraca(1- r^n)1 - r, r eq 1)

If (r = 1),

(S_n = na)

Considering the over shelp piggy bank difficulty, the amount of the GP is uncovered in the following means.


Sum of a GP

Keep in mind the ball being dropped from a height over in the computer animation listed below.

Adsimply its height(a) and also time(r) in the sliders shown at the optimal.

The sphere loses its power and also the sequence of maximum heights is approximately geometric.

Find the full time taken by it from its bounce time to the time it comes toremainder.


1) Consider theGP of this ancestral tree.

The terms are: <1, 2, 4, 8,16,...>

We have actually (a = 1), and (r = 2). Now, let us discover the sum of the initially 12 generations of this GP.

<eginalignS_12 &= dfrac (1) (2^12- 1) 2 - 1\\ &= 2^12- 1\\ &= 4095 ext human being in 12 generationsendalign>


2) Consider another GP:

We have:

Now, the sum of the first 6 terms in this GP will certainly be:

<eginalign&S_6 = dfrac12 dfrac(1-(dfrac13)^6)1- dfrac13 \\&= dfrac12 dfrac(1- dfrac1729)(dfrac23)\\&=dfrac182243\\ &= 0.76endalign>

How to Calculate the Sum of n Terms of a GP?

Sum of Finite GP

Identify the geometric development and also recognize the widespread ratio "r" and also the first term"a".

Find the number of terms "n" for which the sum has to be performed.

Substitutethe values of (a, r, n)in the formula(S_n= dfraca(r^n-1)r - 1) and we calculate the sum of all the regards to the GP.

Sum of Infinite GP

To discover the sum of an limitless Geometric development, we have the initially term and also the consistent ratio in between the terms. We wouldn't understand the last term.Then, (s_n = dfraca_11-r)

If (mid r mid

For example,A square is attracted by joining the midpoints of the sides of the original square. A third square is drawn inside the second square in the same method and also this procedure is continued incertainly. If a side of the initially square is "s" units, identify the amount of locations of all thesquares so formed?


The GP thus created is:

Taking (s^2) out, we get,

Here, (s_n = dfraca_11-r)

Sum of Infinite GP Calculator

Find the simulation listed below. Go into the initially term and also the prevalent ratio and also inspect just how the amount of the infinte GP obtaining converged to a smaller value.

If (mid r mid > 1),then the series does not converge and it has no sum. It is divergent.

For example: Consider the boundless series of thesum of reciprocal of primes,

<-dfrac510+ dfrac1510 -dfrac4510 + dfrac13510+.......>

We discover the initial term is and

The widespread proportion is

Here (mid r mid > 1)that is (3 > 1) and the magnitudes of the terms save getting bigger.

The amount of this GP tends to diverge and also not converge to a worth.


Example 1

In a GP, the sum of the initially three terms is 16, and the amount of the next three terms is 128. Find the sum of the first n regards to the GP.

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Let a and also r be the initially term and the common ratio of GP. We have:

<eginarraylleft{ eginarrayla + ar + ar^2 = 16\ar^3 + ar^4 + ar^5 = 128endarray appropriate.\Rightarrow ,,,left{ eginarraylaleft( 1 + r + r^2 ight) = 16\ar^3left( 1 + r + r^2 ight) = 128endarray est.endarray>

Dividing these two relationswe get,

<eginaligndfracar^3 (1 + r + r^2)a(1 + r+ r^2) = dfrac12816\\Rightarrowr^3 = 8 \\Rightarrowr &= 2endalign>

Substituting this in any type of of the 2 relationships gives (a = frac167). The sum of the first n terms of the GP will be:

( herefore) The sum of n regards to this GP (=dfrac16(2^n-1)7)

Example 2

Sara shared a message with 5 unique people at 1 am. At 2 am, each of her friendsshared it via 5 distinctive civilization. Then at 3 pm each of their friends mutual with 5 distinct world. In this sequence, just how many type of distinctive civilization would certainly have received the message by 8 am?



Clearly, we uncover that this is a geometric development as the first term is 5

Usual proportion (= dfrac255 = dfrac12525 = 5)

<eginalignS_8&= dfrac5(5^8- 1)5 - 1 \\&=dfrac5(390624)4\\ &= 5 imes 97656\\&= 488,280 ext peopleendalign>

( herefore) 488,820 civilization would certainly have actually received the message by 8 am.

Example 3

The distance travelled by a ball dropped from a elevation (in inches) are (dfrac1289, dfrac323), 8, 6... What might be the distance traveled by the ballprior to coming to rest?