## Decimals

Today, we are going to take a closer look at the elements that make up the set of natural numbers. If you remember from a previous blog, this set represents all positive integers within the set of real numbers.

All real numbers (which include natural numbers) are made up of one or more digits. The digits we use in our modern numbering system are 0,1,2,3,4,5,6,7,8,9. Note that there are ten numbers that are made up of one digit (0-9). There are ninety two-digit numbers (10-99), and there are one thousand three-digit numbers (100-999). All real numbers can be expressed in this decimal notation, even fractions. This will be looked into in a future blog.

The position of the digits within a numeral is as important as the digits themselves. The numeral “476” is not the same as the numeral “674” even though both numerals use the same three digits: 4, 7, and 6. In order to understand why this is the case, we need to understand the decimal number system. I’ll show the structure of this system by illustrating the number “six hundred and seventy-four” in three different ways.

In this system, each position represents a multiplier used to determine the magnitude of the digit in its slot (A). The rightmost slot in any number has a multiplier of 1. The slot to its left represents a multiplier of 10. The third slot from the right represents a multiplier of 100. Theoretically, this can continue indefinitely.  Very large (or very small) multipliers can also be expressed using scientific notation.Each slot represents a different multiplier that is ten times more than the slot to the right.  Since all the multipliers in this system are multiples of ten, the decimal notation system is also referred to as a base-10 system. The arithmetic expression (B) is a way of expressing the relationship between the multipliers and its digits. The number (C) is a shorthand way of expressing this arithmetic expression.  There are other numerical systems that use a multiplier other than ten.  We’ll explore these systems and their practical applications in a future blog.

## India & Zero

Lets look at one piece of evidence cited in the history of zero. In order to find it, you will have to go to Gwalior, India, the site of an impressive late 15th c. medieval fort which occupies a plateau in the center of the city. On the eastern side of this plateau is a 9th century Hindu temple, the Chatarbjuj temple, which is carved out of one single chunk of stone. It is dedicated to Vishnu, but it is no longer an active site of worship for the Hindu faithful. Just inside the inner chamber, there is a dedication tablet. By accident, it records the oldest use of “0” in India, for which one can assign a definite date (876 AD).

You will find a more detailed and fascinating description of this site in an essay , “All for Nought,” written by Dr. Bill Casselman (University of British Columbia, Math Department) for the American Mathematical Society. You will see many numerical values on display in the temple inscriptions. These are the numbers as they appeared in the dedication tablet. The numbers 4 and 6 were not written in any of these values.

The essay shows that by 876 A. D. our current place-value system with a base of 10 had become part of popular culture in at least one region of India. including the concept of using zero as a placeholder for “nothing.”  There is a high degree of certainty that the decimal place value notation was invented and developed in India from the 1st to 5th century A.D. There were many number systems simultaneously being used by various cultures throughout Asia and Europe during that time. The knowledge of this system spread from India in a very indirect and complicated way to western Europe via Persian and Arabic mathematicians. Many refer to the decimal place value notation we use today as the Hindu-Arabic number system.

## Sets and Elements

Human beings love to categorize things. Just look at all the nouns we have to describe groups of things in many ways. Our ability to categorize objects evolves out of our mental ability to notice the differences and similarities between two objects. The somewhat unconscious application of this skill gives us a chance to mentally focus on and communicate about many things at once. There is a visually mathematical way of representing the concept. A “collection of well-defined and distinct objects” is referred to as a set (B,C). It’s like the collections of marbles within the white circle (A).  Each of the objects within a given set is  an element. We can express these collections as a rule which describes the attributes common to all elements of the set. Visually, we traditionally use circles or ellipses (I believe any closed shape can be used) to represent the relationships between multiple sets. The resulting diagram is commonly known as a Venn diagram (D). The rectangle enclosing the sets represents the universal set. We’ll explore the most common relationships between sets in a future blog….

Mathematics, like most subjects, is rich in terms and vocabulary. In many cases, there is some fascinating history behind the words we commonly use to express ourselves mathematically. For example, the Venn diagram is named after John Venn (1834-1923), a British logician and philosopher, and a fellow of the Royal Society. Among the many things he did during his life, he published three texts on the subject of logic and he introduced Venn diagrams in his second book Symbolic Logic (1881).

This work was uniquely commemorated in a stained glass window which is on display in the dining hall of his alma mater, Gonville and Caius College, a college in the University of Cambridge, England. Read about his life online and explore his accomplishments. You will find out that he, like most mathematicians, are interested in a variety of things.