Determining Real and Complex Numbers

Oct 13, 2025 by wbrum.org 53 views

Introduction

In mathematics, numbers can be classified into two main categories: real numbers and complex numbers. Real numbers are those that can be represented on the number line, whereas complex numbers are those that have both real and imaginary parts. In this article, we will explore the concept of real and complex numbers and determine which expressions represent purely real numbers and which expressions represent non-real complex numbers.

What are Real Numbers?

Real numbers are those numbers that can be represented on the number line. They are denoted by the symbol R and include all rational and irrational numbers. Examples of real numbers include 3, -5, π, and √2. Real numbers can be positive, negative, or zero.

What are Complex Numbers?

Complex numbers are those numbers that have both real and imaginary parts. They are denoted by the symbol C and are typically represented in the form a + bi, where a is the real part and bi is the imaginary part. The imaginary unit i is defined as the square root of -1. Examples of complex numbers include 3 + 4i, -2 - 3i, and 1 + √2i.

Determining Real and Complex Numbers

To determine whether an expression represents a real or complex number, we need to simplify the expression and check if it has any imaginary part. If the expression simplifies to a number without any imaginary part, it is a real number. If the expression simplifies to a number with an imaginary part, it is a complex number.

Expression 1: $2-\sqrt{-49}$

To simplify this expression, we need to evaluate the square root of -49. Since the square root of a negative number is an imaginary number, we can rewrite -49 as (i^2) * 49, where i is the imaginary unit. Therefore, the square root of -49 is equal to i√49.

\sqrt{-49} = \sqrt{(i^2) * 49} = i\sqrt{49} = 7i

Now, we can substitute this value back into the original expression:

2 - \sqrt{-49} = 2 - 7i

Since this expression has an imaginary part, it represents a complex number.

Expression 2: $\sqrt{(-18)^2}$

To simplify this expression, we need to evaluate the square root of (-18)^2. Since the square of any number is always positive, we can rewrite (-18)^2 as 18^2.

\sqrt{(-18)^2} = \sqrt{18^2} = 18

Since this expression simplifies to a number without any imaginary part, it represents a real number.

Expression 3: $4-32i^2$

To simplify this expression, we need to evaluate the square of i. Since i^2 is equal to -1, we can rewrite 32i^2 as -32.

4 - 32i^2 = 4 - 32(-1) = 4 + 32 = 36

Since this expression simplifies to a number without any imaginary part, it represents a real number.

Conclusion

In conclusion, we have determined which expressions represent purely real numbers and which expressions represent non-real complex numbers. Expression 2, $\sqrt{(-18)^2}$ , represents a real number, while expressions 1 and 3, $2-\sqrt{-49}$ and $4-32i^2$ , represent complex numbers.

Real Numbers

$\sqrt{(-18)^2} = 18$

Complex Numbers

$2-\sqrt{-49} = 2 - 7i$
$4-32i^2 = 36$

Q: What is the difference between real and complex numbers?

A: Real numbers are those numbers that can be represented on the number line, whereas complex numbers are those that have both real and imaginary parts.

Q: What are some examples of real numbers?

A: Some examples of real numbers include 3, -5, π, and √2.

Q: What are some examples of complex numbers?

A: Some examples of complex numbers include 3 + 4i, -2 - 3i, and 1 + √2i.

Q: How do I determine whether an expression represents a real or complex number?

A: To determine whether an expression represents a real or complex number, you need to simplify the expression and check if it has any imaginary part. If the expression simplifies to a number without any imaginary part, it is a real number. If the expression simplifies to a number with an imaginary part, it is a complex number.

Q: What is the imaginary unit i?

A: The imaginary unit i is defined as the square root of -1. It is used to represent the imaginary part of a complex number.

Q: Can you give an example of how to simplify an expression with i?

A: Yes, consider the expression $2-\sqrt{-49}$ . To simplify this expression, we need to evaluate the square root of -49. Since the square root of a negative number is an imaginary number, we can rewrite -49 as (i^2) * 49, where i is the imaginary unit. Therefore, the square root of -49 is equal to i√49.

\sqrt{-49} = \sqrt{(i^2) * 49} = i\sqrt{49} = 7i

Now, we can substitute this value back into the original expression:

2 - \sqrt{-49} = 2 - 7i

Q: What is the difference between a real number and a complex number in terms of their graphical representation?

A: Real numbers can be represented on the number line, whereas complex numbers are represented in the complex plane, which is a two-dimensional plane with real and imaginary axes.

Q: Can you give an example of how to represent a complex number in the complex plane?

A: Yes, consider the complex number 3 + 4i. To represent this number in the complex plane, we need to plot the point (3, 4) on the complex plane, where the x-axis represents the real part and the y-axis represents the imaginary part.

Q: What are some common operations that can be performed on real and complex numbers?

A: Some common operations that can be performed on real and complex numbers include addition, subtraction, multiplication, and division.

Q: Can you give an example of how to add two complex numbers?

A: Yes, consider the complex numbers 2 + 3i and 4 - 2i. To add these numbers, we need to add the real parts and the imaginary parts separately.

(2 + 3i) + (4 - 2i) = (2 + 4) + (3i - 2i) = 6 + i

Q: What are some common applications of real and complex numbers?

A: Real and complex numbers have many applications in mathematics, science, and engineering, including algebra, geometry, calculus, physics, and electrical engineering.

Conclusion

In conclusion, we have answered some frequently asked questions about real and complex numbers. We hope that this article has provided a better understanding of the concept of real and complex numbers and their applications.