## Real Numbers

Natural numbers are counting numbers. Counting refers to things. Counting starts from 1 and goes “one more” forever.

Whole numbers include the additional idea of “nothing” as the absolute reference point. This reference point exists at the beginning of the number line as zero (0). One may then count forever starting from 0. Thus, whole numbers include natural numbers.

### Whole number           =        0 + natural number     (in absolute sense)

Integers include the idea of a relative reference point. This reference point may exist anywhere on the number line. This reference point is also called “zero”, and one counts from this point forever in either direction. Counting to the right is positive. Counting to the left is negative. Thus, integers include whole numbers.

### Negative number      =        0 – natural number     (in relative sense)

Rational numbers fill the gaps between integers on the number line, such as, between 0 and 1, between 1 and 2, etc. These numbers are represented as a ratio of two integers, such as, “1/2”, “2/3”, “7/4”, etc. Rational numbers include all integers. Rational numbers may be represented by decimal numbers that either are recurring or terminate.

### Rational number       =        ratio of two integers

Irrational numbers also fill the gaps between integers, but they cannot be represented as ratio of two integers. Example of irrational number is the “circumference to diameter ratio” of a circle. This is known as “π (pi)”. Other examples are square roots of prime numbers, such as, √2, √3, etc. Irrational numbers may be approximated by decimal numbers of any length.

All the above numbers together make up the set of Real Numbers. The squares of real numbers are always positive and never negative. The square roots of negative numbers are represented by Imaginary numbers.

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• Chris Thompson  On February 9, 2014 at 9:11 PM

• vinaire  On February 9, 2014 at 9:15 PM

No. Imaginary numbers are not real.

• vinaire  On February 9, 2014 at 9:13 PM

But zero is unique. It is not like the counting numbers.

Zero adds an abstract aspect to the numbers.

Zero cannot be defined quantitatively.

Qualitatively, zero may be used as a reference point.

But, zero can have any number of qualities.

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• Chris Thompson  On February 9, 2014 at 9:14 PM

Why is 0 not placed inside the brackets of the set of whole numbers?

• vinaire  On February 9, 2014 at 9:18 PM

0 and {1, 2, 3, …} = {0, 1, 2, 3, …}

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• MarkNR  On February 9, 2014 at 11:51 PM

The philosophy of mathematics can get a bit circular, (empty set) but the principals of arithmetic are invaluable to logical thinking.

• vinaire  On February 10, 2014 at 5:53 AM

A SET is a collection of items. When there is no item in a set then it would be an empty set.

But when a set contains 0 as a number, 0 is looked upon as an item. A set containing 0 is not an empty set.