Problem 36 - Precalculus : Building Concepts and Connections

Question

Find the complex conjugate of each number. $$i^{3}$$

Step-by-Step Solution

Answer

The complex conjugate of \(i^{3}\) is \(i\).

Step 1: Simplify \(i^{3}\)

First you have to calculate the value of \(i^{3}\). By definition, \(i^{3} = i^{2} * i = -1 * i = -i\). Thus, \(i^{3}\) simplifies to \(-i\).

Step 2: Find the complex conjugate

The complex conjugate of a complex number \(a + bi\) is \(a - bi\). The given number is \(-i\), which can be rewritten as \(0 - i\) or \(0 - 1i\). Hence, the complex conjugate is \(0 - (-1)i\) or \(0 + 1i\), which is simply \(i\).

Key Concepts

Complex Numbers

Complex numbers are an extension of the real numbers, represented in the form \(a + bi\), where \(a\) is the real part, and \(bi\) is the imaginary part. Complex numbers enable us to solve equations that have no real number solutions, such as \(x^2 + 1 = 0\).

A complex number combines a real component and an imaginary component. The imaginary component involves the unit \(i\), which is defined as the square root of \(-1\).

• Real Part: The number \(a\) in \(a + bi\) is called the real part.
• Imaginary Part: The number \(b\) times the imaginary unit \(i\) is the imaginary part.

With complex numbers, we can perform addition, subtraction, multiplication, and division similarly to real numbers, but keeping in mind the properties of \(i\), especially \(i^2 = -1\).

Imaginary Unit

The imaginary unit, denoted by \(i\), is a mathematical concept that allows us to work with the square roots of negative numbers. It is defined by the equation \(i^2 = -1\). This definition makes \(i\) unique because no real number squared results in a negative number.

Using \(i\), we can express numbers that involve the square roots of negatives, which are not possible with just real numbers. The powers of \(i\) cycle in a predictable pattern:

• \(i^1 = i\)
• \(i^2 = -1\)
• \(i^3 = -i\)
• \(i^4 = 1\), after which the cycle repeats

Understanding the cycle of powers of \(i\) is crucial when simplifying expressions with complex numbers.

Simplification of Expressions

Simplification of expressions involving complex numbers often leverages the predictable patterns of powers of \(i\), as well as properties of complex arithmetic.

When simplifying expressions, it is essential to:

• Work with the multiplication and division properties of the imaginary unit \(i\).
• Utilize the standard form of a complex number, \(a + bi\), to identify and express the real and imaginary parts clearly.

To find the complex conjugate, we utilize the property that the complex conjugate of a number \(a + bi\) is \(a - bi\).
This process helps remove the imaginary part when multiplying by its conjugate, leading to real-number results.
For instance, simplifying \(i^3\) led us to \(-i\). Its complex conjugate, following the definition, would be \(i\), since changing the sign on the imaginary part results in the expression \(0 + i\).

This simplification is essential in various mathematical contexts, especially when simplifying fractions with complex numbers in the denominator.