# Pi Day Celebration: White House Wishes 'Happy Pi Day'

Today is Pi Day, a day that celebrates the mathematical constant 3.14 or "Pi" represented by the Greek letter "π". Mathematicians began using the Pi symbol in 1706 to represent the ratio of a circle's circumference to its diameter.

The use of Pi is found in ancient times in written references of Egypt and Babylon. Egyptians, when building the Great Pyramid at Giza in 2589-2566 BC, may have used Pi to calculate measurements.

The ratio of the linear measurements is approximately equal to 2π with its 1760 cubit perimeter and height of 280 cubits (1760/280= 6.2857). These calculations suggest that Egyptians purposely designed the pyramid with the proportions of a circle in mind. A clay tablet from Babylon dating back to 1900-1600 BC showed a geometrical reference of 25/8 =3.1250, that relates to Pi.

We've all used the irrational number Pi to solve trigonometry and geometry problems. Pi's value consists of an infinitely repeating decimal. An extended representation of the decimal was discovered by mathematicians and scientists in 2011 of over 10 trillion digits. The discovery was solely for record-breaking purposes, since no more than 40 Pi digits are usually required for scientific applications.

Pi is also used in other sciences, including cosmology, statistics, thermodynamics and mechanics. The San Francisco Exploratorium unofficially began celebrating Pi Day in 1988. The House of Representatives designated March 14 as "Pi Day" in 2009, making it official. In celebration of Pi Day, the White House's Twitter page posted a photo of President Obama with a kid stuffing his face with pie and the words "Happy Pi Day."