# What is the name for half of pi?

March 14, or 3/14, is

**known as**“**Pi**Day” because of its resemblance to the first three digits in the decimal expansion of $**pi**$ (**pi**), which is defined as the ratio of a circle's circumference to its diameter: The true circle constant is the ratio of a circle's circumference to its radius, not to its diameter.A.

### Why do they call it PI?

It was first

**called**"**pi**" in 1706 by [the Welsh mathematician] William Jones, because**pi**is the first letter in the Greek word perimitros, which means "perimeter." It's a special number.#### Why do you use pi?

**Pi**(π), the 16th letter of the Greek alphabet,**is**used to represent the most widely known mathematical constant. By definition,**pi is**the ratio of the circumference of a circle to its diameter. In other words,**pi**equals the circumference divided by the diameter (π = c/d).#### When was Pi proven to be irrational?

In the**18th century**, Johann Heinrich Lambert proved that the number π (pi) is irrational: that is, it cannot be expressed as a fraction a/b, where a is an integer and b is a non-zero integer.#### Why is Piscine called pi?

He reflects on his**name**, which is**Piscine**Molitor Patel, and says that he was**named**after a swimming pool.**Pi's**parents did not like water, but they had a family friend who was a former champion swimmer. This man was**named**Francis Adirubasamy, but**Pi**called him Mamaji, which is similar to “uncle.”

B.

### What is the meaning of 2pi?

Euler is the first person who started to use radian in trigonometry. The circumference of a unit circle is

**2pi**, therefore he defined 360 degrees be**2pi**radian. A radian is the measure of an angle subtended at the centre of a circle by an arc equal in length to the radian.#### What is 4pie?

The expression**4Pi**may refer to: IBM System/**4 Pi**, a family of avionics computers.**4Pi**microscope, a microscope that uses interference and fluorescence computers. 4×π = 12.56637, the solid angle of a complete sphere measured in steradians.**4Pi**Reprap controller.#### What is the symbol for 2pi?

Hence, anyone could use**pi**when they had a calculation involving half of**tau**."**Tau**, the 19th letter of the Greek alphabet, was chosen independently as the symbol for 2pi by Michael Hartl, physicist and mathematician and author of "**The Tau Manifesto**," and Peter Harremoës, a Danish information theorist.#### What is the ratio of the circumference of a circle?

The ratio of circumference of circle to its diameyer is the number π ,a mathematical constant, commonly approximated as**3.14159**. It has been represented by the Greek letter "π" since the mid-18th century, though it is also sometimes spelled out as "pi".

Updated: 11th December 2019