## Introduction to Real Numbers

Real numbers are the set of numbers that include all rational and irrational numbers on the number line. Real numbers can be positive, negative, or zero. They can also be integers, fractions, decimals, or roots of numbers. In this article, we will explore the concept of real numbers and identify which of the following is not a real number.

## List of Types of Numbers

Before we identify which of the following is not a real number, let’s first understand the different types of numbers that exist:

**Natural Numbers:**These are the counting numbers, starting from 1 and going up infinitely (1, 2, 3, 4, …).**Whole Numbers:**These include all the natural numbers along with zero (0, 1, 2, 3, …).**Integers:**Integers are whole numbers, along with their negative counterparts and zero (… -3, -2, -1, 0, 1, 2, 3 …).**Rational Numbers:**These are numbers that can be expressed as fractions, where the numerator and denominator are integers (e.g., 1/2, -3/4, 5).**Irrational Numbers:**These numbers cannot be expressed as fractions and have non-repeating, non-terminating decimal representations (e.g., π, √2).

## Identifying Which Of The Following Is Not A Real Number

Now let’s analyze which of the following is not a real number:

**Imaginary Numbers:**Imaginary numbers are multiples of the imaginary unit “i,” where i² = -1. Examples of imaginary numbers include 2i, -5i, and √(-9). Imaginary numbers exist in the complex number system, which includes both real and imaginary parts. Since imaginary numbers do not lie on the real number line, they are not considered real numbers.**Complex Numbers:**Complex numbers are a combination of real and imaginary numbers. They are represented in the form a + bi, where “a” is the real part, and “bi” is the imaginary part. Examples of complex numbers include 3 + 4i, -2 – i, and 6i. Complex numbers include real numbers as a subset but also incorporate imaginary numbers, making them distinct from real numbers.**Infinity:**Infinity (∞) is a concept rather than a specific number. It represents an unbounded quantity that is greater than any finite number. Infinity is not a real number because it cannot be assigned a precise value on the number line. It is used in calculus and higher mathematics to denote limitless quantities.**Undefined Numbers:**Undefined numbers arise when certain mathematical operations result in indeterminate forms. For example, division by zero (0/0) or taking the square root of a negative number (√(-4)) leads to undefined results. These expressions do not have a well-defined real number value, making them distinct from real numbers.

## Conclusion

In conclusion, while real numbers encompass a broad range of numbers on the number line, there are certain types of numbers that do not fall under the category of real numbers. Identifying which of the following is not a real number involves understanding concepts such as imaginary numbers, complex numbers, infinity, and undefined numbers. By distinguishing between these different types of numbers, we can develop a clearer understanding of the diverse numerical systems that exist in mathematics.