Happy Pie Day, Everyone! What is Pie Day? Pi Day is an annual celebration of the mathematical constant π (pi). Pi Day is observed on March 14 (3/14 in the month/day format) since 3, 1, and 4 are the first three significant digits of π.[2][3] In 2009, the United States House of Representatives supported the designation of Pi Day.[4] Pi Approximation Day is observed on July 22 (22/7 in the day/month format), since the fraction 22⁄7 is a common approximation of π, which is accurate to two decimal places and dates from Archimedes.[5]
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