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# Complex Number Formula: Identities, Representation, Examples

Complex Number Formula are number combines a real part (a) and an imaginary part (b), written as a + ib, where 'a' is Re(z), 'b' is Im(z), and 'ib' is the imaginary part. Complex Number Formula are a mathematical concept used to address the problem of finding the square root of negative numbers. The idea of complex numbers has a historical background that dates back to the 1st century when a Greek mathematician, Hero of Alexandria, attempted to calculate the square root of a negative number. At that time, he essentially converted the negative number into a positive one and computed its square root. However, the true nature of complex numbers was not fully understood until the 16th century when Italian mathematician Gerolamo Cardano made significant contributions. Cardano worked on solving negative roots of cubic and quadratic polynomial expressions, which led to the development of complex numbers.

Complex numbers find applications in various scientific fields, including signal processing, electromagnetism, fluid dynamics, quantum mechanics, and vibration analysis. In the study of complex numbers, one can explore their definition, terminology, visualization, properties, and operations, which are all crucial components of this mathematical concept.

Also Check – Introduction to Euclid Formula

## What are Complex Numbers?

A complex number can be defined as the combination of a real number and an imaginary number. It takes the form a + ib and is typically denoted as ‘z,’ where ‘a’ and ‘b’ are both real numbers. The ‘a’ value is referred to as the real part of the complex number and is denoted as Re(z), while ‘b’ is termed the imaginary part and is denoted as Im(z). The component ‘ib’ is known as an imaginary number. Examples of complex numbers include numbers like 2 + 3i, -2 – 5i, 12 + i√32, and so on. These are all instances of complex numbers that consist of both real and imaginary components.

Power of “i”

The symbol “i” represents the imaginary unit and is instrumental in denoting the imaginary component of complex numbers. It plays a crucial role in dealing with the square roots of negative numbers. Specifically, we have the value of i² = -1, which is fundamental in the realm of complex numbers. This relationship allows us to find the square root of -4 as follows:

√(-4) = √(i² * 4) = √(i²) * √4 = (±i) * 2 = ±2i

The pattern of powers of “i” follows these rules:

i = √(-1)

i² = -1

i³ = i * i² = i * (-1) = -i

i⁴ = (i²)² = (-1)² = 1

For any integer “n,” i(4n) = 1

For any integer “n,” i(4n + 1) = i

For any integer “n,” i(4n + 2) = -1

For any integer “n,” i(4n + 3) = -i

These relationships help in simplifying expressions involving powers of “i” in various mathematical contexts, including complex number calculations.

Also Check – Triangles Formula

## Graphing of Complex Numbers

A complex number is composed of two essential parts: the real part and the imaginary part, which can be thought of as an ordered pair (Re(z), Im(z)). This ordered pair representation allows complex numbers to be visualized as coordinates on the Euclidean plane. In the context of complex numbers, this plane is referred to as the complex plane or the Argand Plane, named after Jean-Robert Argand, a Swiss mathematician.

When representing a complex number, such as z = a + ib, on the complex plane, the real part ‘a’ corresponds to the position along the x-axis, and the imaginary part ‘ib’ corresponds to the position along the y-axis. This representation enables us to visualize complex numbers in a manner similar to plotting points on a Cartesian coordinate plane.

Two crucial terms related to the representation of complex numbers on the Argand Plane are:

Modulus: The modulus of a complex number ‘z,’ denoted as |z| or sometimes simply as ‘r,’ represents the distance of the complex number from the origin (0, 0) in the complex plane. It is calculated as the square root of the sum of the squares of the real and imaginary parts: |z| = √(a² + b²). The modulus provides information about the magnitude or absolute value of the complex number.

Argument: The argument of a complex number ‘z,’ denoted as arg(z) or θ, represents the angle that the line connecting the complex number to the origin makes with the positive real axis (x-axis) in the complex plane. The argument is usually measured in radians. It provides information about the direction or orientation of the complex number.

Understanding these two important terms, modulus and argument, is crucial for fully characterizing and working with complex numbers in the Argand Plane. They provide a geometric interpretation of complex numbers and are fundamental in various mathematical applications involving complex numbers. ## Polar Representation of a Complex Number

By utilizing the modulus and argument of a complex number, along with its representation on the Argand Plane, we can introduce a different way of representing complex numbers known as the polar form of a complex number. For a complex number z = a + ib, its polar form can be expressed as z = r(cos(θ) + isin(θ)), where:

‘r’ represents the modulus (r = √(a² + b²)).

‘θ’ signifies the argument of the complex number (θ = arctan(b/a)).

In this polar form, ‘r’ represents the magnitude or distance of the complex number from the origin in the complex plane, while ‘θ’ represents the angle that the line connecting the complex number to the origin makes with the positive real axis (measured in radians). This representation, based on trigonometric functions, offers a different perspective on complex numbers and is particularly useful for certain mathematical operations and applications, such as complex number multiplication and division.

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## Properties of a Complex Number

Complex numbers exhibit various properties and characteristics that are essential in mathematical and engineering contexts. Here are some important properties of complex numbers:

Closure: Complex numbers are closed under addition, subtraction, multiplication, and division. When you perform these operations on complex numbers, the result is always another complex number.

Conjugate: The conjugate of a complex number z = a + ib is denoted as z̅ (pronounced “z-bar”) and is defined as z̅ = a – ib. The conjugate reflects the complex number over the real axis in the complex plane. It has the property that z * z̅ = |z|², where |z| is the modulus of z.

The conjugate of a complex number is formed by keeping the real part the same and changing the sign of the imaginary part. If the sum and product of two complex numbers result in real numbers, then these complex numbers are called conjugate complex numbers. For a complex number z = a + ib, its conjugate is denoted as z̅ and is equal to a – ib.

The sum of a complex number and its conjugate is given by:

z + z̅ = (a + ib) + (a – ib) = 2a

The product of a complex number and its conjugate is given by:

z * z̅ = (a + ib) * (a – ib) = a² + b²

## Ordering of Complex Numbers

Complex numbers cannot be ordered in the same way that real numbers can be ordered. Unlike real numbers and other related number systems, complex numbers lack the structure of an ordered field. There is no way to establish an ordering of complex numbers that is compatible with both addition and multiplication operations.

Furthermore, in an ordered field, the non-trivial sum of squares (i.e., not equal to zero) always results in a number that is not zero. However, in the realm of complex numbers, the non-trivial sum of squares can equal zero, as demonstrated by the equation i² + 1² = 0.

Complex numbers are often represented and measured in a two-dimensional Argand plane, where their magnitude corresponds to their distance from the origin. This approach provides a geometric understanding of complex numbers.

Euler’s formula plays a significant role in representing complex numbers in the coordinate plane. According to Euler’s formula, for any real value θ, we have eiθ = cosθ + isinθ. This formula represents a complex number in the coordinate plane, where cosθ is the real part (aligned with the x-axis), sinθ is the imaginary part (aligned with the y-axis), and θ is the angle formed with respect to both the x-axis and the line connecting the origin to the complex number.

Euler’s formula can also be used to express the exponential function in terms of its real and imaginary components: ex + iy = ex(cosy + isiny). This decomposition separates the exponential function into its real and imaginary parts, providing insights into complex number operations and calculations.

Modulus: The modulus (absolute value) of a complex number z = a + ib is denoted as |z| and is calculated as |z| = √(a² + b²). The modulus represents the distance of the complex number from the origin in the complex plane.

Argument: The argument of a complex number z = a + ib is denoted as arg(z) and is the angle (in radians) that the line connecting the complex number to the origin makes with the positive real axis. The argument is typically measured counterclockwise.

Polar Form: Complex numbers can be represented in polar form as z = r(cos(θ) + isin(θ)), where r is the modulus and θ is the argument.

Exponential Form: Complex numbers can also be expressed in exponential form as z = |z|e^(iθ), where e is the base of natural logarithms. This form is particularly useful for complex number multiplication and division.

Addition and Subtraction: To add or subtract complex numbers, simply add or subtract their real and imaginary parts separately.

Multiplication: To multiply two complex numbers z₁ = a + ib and z₂ = c + id, use the distributive property and the fact that i² = -1: z₁ * z₂ = (a + ib)(c + id) = (ac – bd) + i(ad + bc).

Division: To divide two complex numbers z₁ and z₂, multiply the numerator and denominator by the conjugate of the denominator to simplify the expression: z₁ / z₂ = (z₁ * z̅₂) / (z₂ * z̅₂).

Roots: Complex numbers can have multiple roots, and finding the roots of complex numbers involves solving equations like zⁿ = a, where ‘n’ is a positive integer.

Algebraic Operations: Complex numbers obey the same algebraic laws as real numbers, including commutativity, associativity, and distributivity.

These properties make complex numbers a powerful tool in various mathematical and scientific disciplines, such as engineering, physics, and signal processing, where they are used to model and analyze a wide range of phenomena.

## Algebraic Identities of Complex Numbers

All algebraic identities that apply to real numbers also hold true for complex numbers. Complex numbers can be manipulated using algebraic identities, including addition, subtraction, and exponentiation. Here are some common algebraic identities involving complex numbers:

• Square of Sum: (z₁ + z₂)² = z₁² + 2z₁z₂ + z₂²
• Square of Difference: (z₁ – z₂)² = z₁² – 2z₁z₂ + z₂²
• Cube of Sum: (z₁ + z₂)³ = z₁³ + 3z₁²z₂ + 3z₁z₂² + z₂³
• Cube of Difference: (z₁ – z₂)³ = z₁³ – 3z₁²z₂ + 3z₁z₂² – z₂³
• Product of Sum and Difference: (z₁ + z₂)(z₁ – z₂) = z₁² – z₂²
• Square of a Complex Number: z² = z * z (where z is any complex number)
• Square of a Sum with Three Terms: (z₁ + z₂ + z₃)² = z₁² + z₂² + z₃² + 2z₁z₂ + 2z₁z₃ + 2z₂z₃

These algebraic identities are valuable for solving equations, simplifying expressions, and performing various mathematical operations involving complex numbers. They are particularly useful in complex analysis and engineering applications where complex numbers are employed to model and analyze real-world phenomena.

Also Check – Congruence of Triangles Formula

## Complex Numbers Tips and Tricks

All real numbers are indeed a subset of complex numbers, but not all complex numbers are real numbers. Real numbers can be considered as a special case of complex numbers where the imaginary part is zero. On the other hand, complex numbers can have both real and imaginary parts.

Similarly, all imaginary numbers are a subset of complex numbers, but not all complex numbers are imaginary. Imaginary numbers are complex numbers with a real part equal to zero.

The conjugate of a complex number z = a + ib is represented as z̅ = a – ib. This involves changing the sign of the imaginary part while keeping the real part unchanged.

The magnitude (or modulus) of a complex number z = a + ib is denoted as |z| and is calculated as |z| = √(a² + b²). It represents the distance of the complex number from the origin in the complex plane and is always a non-negative real number.

## Examples Using Complex Number Formula

Example 1: Let’s calculate the sum of 4 – 6i and -2 + 4i using the complex number formula.

Solution:

(4 – 6i) + (-2 + 4i) = (4 – 2) + i(-6 + 4) = 2 – 2i

Answer: The sum is 2 – 2i.

Example 2: Now, we’ll find the product of 1 + 2i and its conjugate using the complex number formula.

Solution:

(1 + 2i) × (1 – 2i) = 1 × 1 + 1 × (-2i) + 2i × 1 + 2i × (-2i) = 1 – 2i + 2i – 4i²

Since i² = -1, we can simplify:

1 – 2i + 2i + 4 = 1 + 4 = 5

## Complex Number Formula FAQs

### What is meant by Complex Number?

A complex number is expressed in the form a + bi, where "a" is the real part and "b" is the imaginary part.

### Does 0 is a complex Number?

Based on the definition of complex numbers, we can conclude that 0 is indeed both a complex number and a real number.

### Define the conjugate of a complex number.

The conjugate of a complex number z = a + ib is denoted as z̅ (pronounced "z-bar") and is defined as z̅ = a - ib.

### Define the Modulus of complex numbers.

The modulus (absolute value) of a complex number z = a + ib is denoted as |z| and is calculated as |z| = √(a² + b²).