A geometric progression is a sequencewhere every term bear a consistent ratioto its preceding term. Geometric development is a special type of sequence. In order to get the next term in the geometric progression, we need to multiply with afixed term well-known as the common ratio,every time, and also if we want to find the coming before term in the sequence, we just have to divide the term through the same usual ratio. Right here is anexample that a geometric progression is 2, 4, 8, 16, 32, ...... Having a usual ratio the 2.

You are watching: What is the sum of the geometric sequence −1, 6, −36, … if there are 7 terms?

The geometric progressions deserve to be a finite series or an unlimited series. The common ratio of a geometric progression can be a an adverse or a confident integer. Here we chandelier learn more about the geometric progression formulas, and also the different types of geometric progressions.

1.Geometric progression Introduction
2.Geometric development Formula
3.Geometric progression Sum Formula
4.Geometric progression Examples
5.Practice questions on Geometric Progression
6.FAQs ~ above Geometric Progression

Geometric progression Introduction

A geometric development is a special kind of sequencewhere the successive terms be affected by each other a consistent ratio recognize as a common ratio. Geometric development is likewise known as GP. The geometric succession is generally represented in form a, ar, ar2.... Whereby a is the an initial term and r is the typical ratioof the sequence. The typical ratio have the right to have both an adverse as well as confident values.To uncover the regards to a geometric series, we only require the very first termand the constant ratio.


The geometric progression isof 2 types. The two varieties of geometric progressions are based upon the number of terms in the development series. The two species of a geometric progression are the finite geometric progression and also the limitless geometric progression. The details that the two geometric progressions room as follows.

Finite geometric progression

Finite geometric progression is the geometric series that contains a finite variety of terms. That is the sequence wherein the critical term is defined. For instance 1/2,1/4,1/8,1/16,...,1/32768 is a limited geometric series where the last term is 1/32768.

Infinite geometric progression

Infinite geometric development is the geometric series that includes an infinite number of terms. It is the sequence wherein the critical term is not defined. For example, 3, −6, +12, −24, +... Is one infinite collection where the last term is not defined.

Geometric progression Formula

The geometric development formula is provided to discover the nth hatchet in the sequence. To uncover the nth ax in the geometric progression, we need the very first term and also the common ratio. If the typical ratio is not known, the typical ratio is calculate by recognize the proportion of any type of term by its preceding term.The formula because that the nth term of the geometric development is:

(a_n) = arn-1


a is the very first termr is the usual ration is the variety of the ax which we desire to find.

Geometric development Sum Formula

The geometric development sum formula is supplied to uncover the amount of all the state in a geometric sequence. As we review in the over section the geometric sequenceis of two types, finite and also infinite geometric sequences, therefore the sumof their termsis likewise calculated by different formulas.

Finite Geometric Series

If the variety of terms in a geometric succession is finite, climate the amount of the geometric collection is calculate by the formula:

(S_n) = a(1−rn)/(1−r) forr≠1, and

(S_n) = an because that r = 1


a is the first termr is the typical ratio n is the variety of the state in the series

Infinite Geometric Series

If the variety of terms in a geometric sequence is infinite,an boundless geometricseries amount formula is used. In infinite series, there arise two instances depending ~ above the value of r. Let us discuss the infinite collection sum formula because that the 2 cases.

Case 1: When|r| a is the very first termr is the common ratio

Case 2:|r| >1

In this case, the collection does not converge and also it has no sum.

Geometric progression vs Arithmetic Progression

Here are a few differences in between geometric progression and also arithmetic progression presented in the table below:

Geometric ProgressionArithmetic Progression
GP has actually the same common ratio throughout.AP does no have usual ratio.
GP does not have typical difference.AP has actually the same common difference throughout.
A brand-new term is the product of the previous term and also the common ratioA brand-new term is the enhancement of the ahead term and also the usual difference.
An unlimited geometric sequence is one of two people divergent or convergent.An limitless arithmetic succession is divergent.
The sports of the state is non-linear.The sport of the terms is linear.

Important note on Geometric Progression

In a geometric progression, each succeeding term is acquired by multiplying the usual ratio come its preceding term.

The formula because that the nthterm of a geometric progression whose first term is aand common ratio is (r) is: (a_n=ar^n-1)

The amount of n state in GP whose very first term is aand the common ratio is rcan it is in calculated usingthe formula: (S_n=dfraca(1-r^n)1-r)

The sum of unlimited GP formula is provided as: (S_n=dfraca1-r) where |r|

Related topics on Geometric Progression

Check out these interesting write-ups related to geometric progression:


Observe the each square is fifty percent of the size of the square beside it. Which sequence does this sample represent?


Let's write the geometric development seriesrepresented in the figure.

1, 1/2, 1/4, 1/8 ...

Every successive term is acquired by dividing its coming before term by 2

The succession exhibits a typical ratio that 1/2.

Answer:The pattern represents the geometric progression.

Question 2: In a details culture, the count of bacteria gets doubled after every hour. There were 3 bacteria in the society initially. What would certainly be the complete count the bacteria at the finish of the 6th hour?


Here, the number of bacteria creates a geometric progression where the first term ais 3 and the usual ratio ris 2.

So, the total number of bacteria at the finish of the sixth hour will be the sum of the very first 6 regards to this progression offered by (S_6).

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(S_6) = 3(26−1)/(2−1)




Answer:So, the full count the bacteria at the finish of the sixth hour will be 189.

Example 3: discover the complying with sum that the terms of this unlimited geometric progression: