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In mathematics, sequences are fundamental concepts, and two of the most common types are Arithmetic Progression (AP) and Geometric Progression (GP). Both sequences are structured arrangements of numbers, but they differ significantly in their formation rules. An Arithmetic Progression is defined by a constant difference between consecutive terms, known as the “common difference.” In contrast, a Geometric Progression is characterized by a constant ratio between successive terms, referred to as the “common ratio.” Understanding the difference between Geometric Progression and Arithmetic Progression is important, as they are foundational in various mathematical applications, including algebra, calculus, and real-world problem-solving scenarios. Questions related to AP and GP are frequently asked in competitive exams like the SAT, GMAT, GRE, JEE, and other standardized tests that assess quantitative aptitude and mathematical reasoning skills.
Table of Contents
What is Geometric Progression?
Geometric Progression (GP) is a sequence of numbers in which each term after the first is found by multiplying the previous term by a fixed, non-zero number called the “common ratio” (denoted by r). The general form of a geometric progression can be written as:
a, ar, ar2, ar3,…
where:
- a is the first term of the sequence.
- r is the common ratio, which can be positive or negative.
Formulas in Geometric Progression
- n-th Term of a Geometric Progression: The n-th term (Tn) of a GP is given by the formula:
| Tn = arn-1 |
where n is the position of the term in the sequence.
- Sum of the First n Terms (Finite GP): The sum Sn of the first n terms of a GP can be calculated using:
| Sn = {a(1-rn)} / (1-r) for r ≠ 1 |
If r=1, the sum is simply:
| Sn = n x a |
- Sum of an Infinite Geometric Series: If ∣r∣<1, the sum S∞ of an infinite GP is:
| S∞ = a / (1-r) |
Properties of Geometric Progression
The most important properties of geometric progression are mentioned here:
- Common Ratio: The ratio between any two consecutive terms is constant. This is the defining property of a GP.
- Product of Terms: The product of the terms equidistant from the beginning and end of a finite GP is constant. For example, in the GP a, ar, ar2, ar3,…arn-1, the product a×arn-1 is the same as ar×arn-2, and so on.
- Geometric Mean: The geometric mean between two terms aaa and bbb is the square root of their product, √ab. In a GP, the middle term of any three consecutive terms is the geometric mean of the other two.
- Exponential Growth or Decay: A geometric progression with r > 1 represents exponential growth, while 0 < r < 1 represents exponential decay. If r < 0, the sequence alternates between positive and negative values.
Also Read: What is the Difference Between Pound and Kilogram?
What is Arithmetic Progression?
Arithmetic Progression (AP) is a sequence of numbers in which the difference between any two consecutive terms is constant. This constant difference is called the “common difference,” denoted by d.
General Form of an Arithmetic Progression:
An arithmetic progression can be represented as: a, a+d, a+2d, a+3d,…
where:
- a is the first term.
- d is the common difference.
Formulas in Arithmetic Progression:
- n-th Term of an Arithmetic Progression: The n-th term (an) of an AP can be calculated using the formula:
| an = a + (n-1) x d |
where:
- an is the n-th term.
- n is the position of the term in the sequence.
- Sum of the First n Terms of an Arithmetic Progression: The sum of the first nnn terms (Sn) of an AP can be calculated using the formula:
| Sn = n/2 x {2a + (n-1) x d} |
or alternatively:
| Sn = n/2 x (a + an) |
where:
- Sn is the sum of the first nnn terms.
- an is the n-th term.
Properties of Arithmetic Progression
The most important properties of arithmetic progression are mentioned here:
- Constant Difference: The difference between any two consecutive terms is always the same, i.e., an+1 − an = d.
- Linearity: The terms of an AP grow (or decrease) linearly, depending on whether the common difference d is positive or negative.
- Symmetry: The middle term of an AP is the average of the first and the last term. For example, in a finite AP, the middle term when n is odd is given by a(n+1)/2, and when n is even, it is the average of the two middle terms.
- Sum Formula: The sum of a finite number of terms can be quickly calculated using the sum formula, which is particularly useful in solving problems related to series and sequences.
- Equal Spacing: The terms in an AP are evenly spaced, which makes it a simple yet powerful concept in various areas of mathematics, such as algebra, calculus, and financial mathematics.
Comparison Between Geometric Progression and Arithmetic Progression
Here’s a comparison between Geometric Progression (GP) and Arithmetic Progression (AP) presented in a tabular form:
| Aspect | Arithmetic Progression (AP) | Geometric Progression (GP) |
| Definition | A sequence in which the difference between consecutive terms is constant. | A sequence in which the ratio between consecutive terms is constant. |
| General Form | a, a+d, a+2d, a+3d,… | a, ar, ar2, ar3,… |
| Common Difference/Ratio | Common Difference (d) | Common Ratio (r) |
| n-th Term Formula | an = a + (n-1) x d | an = arn-1 |
| Sum of First n Terms | Sn = n/2 x {2a + (n-1) x d} | Sn = a x {(rn-1) / (r-1)} for r ≠ 1 |
| Nature of Sequence | Linear sequence | Exponential sequence |
| Graphical Representation | Straight line | Exponential curve |
| Middle Term | Average of the first and last term in a finite AP | Geometric mean of the first and last term in a finite GP |
| Examples | 3, 5, 7, 9, 11,… | 2, 6, 18, 54,… |
| Applications | Used in problems involving linear growth, uniform motion, simple interest, etc. | Used in problems involving exponential growth/decay, compound interest, population growth, etc. |
Also Read: Difference Between Marginal Cost and Average Cost
Application of Geometric Progression and Arithmetic Progression in Real Life
Here’s a table outlining the applications of the difference between Geometric Progression (GP) and Arithmetic Progression (AP) in real life:
| Particular | Arithmetic Progression (AP) | Geometric Progression (GP) |
| Financial Planning | Calculating simple interest, where interest is added linearly. | Calculating compound interest, where interest grows exponentially. |
| Salary Structure | Structured salary increments by a fixed amount each year. | Salary increments by a fixed percentage (e.g., bonuses or raises). |
| Distance & Time | Uniform motion, where distance increases by a fixed amount per unit of time. | Population growth or radioactive decay, where changes occur exponentially over time. |
| Construction | Stairs design, where each step has a uniform rise. | Design of certain architectural elements, such as spirals, where dimensions change exponentially. |
| Scheduling | Adding equal time slots or intervals in schedules. | Scheduling events with exponentially increasing/decreasing intervals (e.g., dosage of drugs in certain medical treatments). |
FAQs
An arithmetic sequence is a sequence of numbers where the difference between consecutive terms is constant. A geometric sequence is a sequence of numbers where the ratio between consecutive terms is constant.
The main difference between AP and GP lies in the way their terms are generated. In AP, the difference between consecutive terms remains constant (called the common difference, d). In GP, the ratio between consecutive terms remains constant (called the common ratio, r).
A geometric progression (GP) is a sequence of numbers where each term after the first is found by multiplying the previous term by a fixed non-zero number called the common ratio (r). An arithmetic progression (AP) is a sequence of numbers where each term after the first is found by adding a fixed number called the common difference (d) to the previous term.
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