The Number π

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The most interesting number that students come across in the Primary curriculum is &pi;. They get to know &pi; as the ratio between the circumference &amp; diameter of a circle. There are many interesting facts about &pi;.

It is also usually said that its value is equal to 3.14. But this is just an approximate value which is sufficient for our daily needs.

We can think of &pi; as a number which relates the length of a straight line (diameter of a circle) to the length of a curve (circumference) related to that straight line.

&pi; was the first mystery number known to all civilizations because the circle was a common figure which had to be drawn for religious and commercial reasons. They know that the ratio between the circumference &amp; the diameter of a circle was a constant. It must have taken a lot of time and many approximations of &pi; in many different sizes of circles, before all civilizations came to the conclusion that the relation between the circumference &amp; diameter was a fixed number for any circle.

After this realization, the most logical step for all civilizations was to find values of &pi; sufficient enough for their practical needs. 3 and &radic;10 were some of the approximations discovered more than 2000 years ago.

As knowledge of mathematics evolved, attempts were made to arrive at more accurate approximate values. 22/7 and 355/113 were some of these values. 355/113  is more accurate than 22/7.

But until 16thcentury, no more understanding was achieved, except that is it an interesting number. &pi; was proved to be an irrational number in 1761 meaning whereby that it cannot be expressed in rational form i.e as a/b where a &amp; b are integers. Irrational numbers turned out to be numbers which could only be expressed as the sum of an infinite series of fractions.

In 1658 it was expressed as a sum of infinite continued fractions. In 1674, Leibniz succeeded in expressing it as the limit of an infinite series with simple fractions and pattern. Then many infinite series were found out whose sum (limit) was &pi;.

&pi; which is pronounced as &ldquo;pie&rdquo; was originally used to represent perimeter. In 1706 it was used by William James to represent the ratio of the circumference to the diameter of a circle. Since then it has become one of the most recognized mathematical symbols.

Expressed in decimal numbers, an irrational number has the following property. The digits in its decimal part never end and do not show any pattern or repetition.

Finding as many digits as possible of &pi; became almost an industry. But scientists have estimated that if we calculate any distance over the curved surface of the Earth, using the value of π up to 15 decimal places, i.e 3.141592653589793, it would be off by a gap 10,000 times thinner than a hair!

Then why do we need to compute the value to many decimal places? This effort was complemented by the invention of computers. The speed of calculating the number of digits of &pi; was used as a measure of the speed of a computer.

An outcome of this effort was the discovery that digits in an irrational number can be used for coding messages so that they are not &ldquo;understandable&rdquo; to anyone who does not have the key. Today messages sent through the internet are scrambled using many techniques which were the result of study of irrational numbers.

In 1882 &pi; was found to belong to a special class of irrational numbers, which were called transcendental numbers.

We know that √2 is an irrational number. But it can be expressed as the solution to the equation x2 = 4 which is an algebraic equation. Hence √2 is called an algebraic irrational number.

Transcendental numbers are a class of irrational numbers which cannot be expressed as solutions of an algebraic equation.

&pi; occurs in unexpected expressions &amp; equations which describe physical phenomena.

We can think of &pi; as a quantity which relates curved lines to straight lines.

Today, with travel even taking place away from the Earth, measuring angles accurately has become very important. Very accurate values of &pi; are required in precise calculation of angles.

Leonard Euler discovered an equation which connects &pi; &amp; e in an equation which according to surveys, is considered the most beautiful equation in all of science.

eiπ= -1

Most countries celebrate 14thMarch every year as Pi Day, because 14thMarch is written (in many countries) as 3.14. May be India should celebrate 22nd July (written as 22/7) as the Indian &pi; Day!

Remembering Digits of π

The following sentences have been constructed to help us remember π to a few decimals. Counting the letters in each word, you can write the value of π.

May I have a large container of coffee?

How I wish I could enumerate?

The English physicist James Jeans wrote this piem: How I want a drink, alcoholic of course, after the heavy lectures involving quantum mechanics. Counting the letters in each word, you can write 3.1415 92653 58979, giving 15 digits of pi, more digits than you are ever likely to need.

&pi; in Indian Mathematics

One of problems of ancient Hindu was the construction of yagnya altars. One of the requirements was the construction of a circular altar whose area was equal to that of a square altar. The early part of the vedic literature assumes a value of 3 for &pi;. The later sulba sutras give the value accurate to many decimals.

Aryabhatta in the 5thcentury worked out a value which was accurate up to 4 decimal places! In the 14thcentury, Madhava worked out the infinite series for &pi;/4 which was discovered by Liebnitz 300 years later. This is never taught in our schools, either in the math or the history class!

Computing Digits of &pi;

Before the invention of modern mathematics, the approach to calculating the value of &pi; was to approximate the circle with a polygon of a huge number of sides. Archimedes is supposed to have arrived at a value of around 3 1/7 by using a polygon with 96 sides!

Ludolph van Ceulen (1540 - 1610), who spent a major part of his life calculating values of &pi; discovered 35 digits in pi by supposing a polygon with literally Billions and Billions of sides.

The calculation of values of &pi; became much easier after the invention of calculus and infinite series.

It became faster with the advent of computer software.

In March 2019, Emma Haruka Iwao, an employee at Google, computed 31.4 trillion digits of pi using y-cruncher and Google Cloud machines. This took 121 days to complete.

In January 2020, Timothy Mullican announced the computation of 50 trillion digits over 303 days.

Calculating more digits of &pi; has become an intellectual as well as a technological challenge. So we can expect more digits of &pi; discovered in the years to come!

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