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The number π (/ p aɪ /; spelled out as "pi") is a mathematical constant that is the ratio of a circle's circumference to its diameter, approximately equal to 3.14159.The number π appears in many formulae across mathematics and physics.
Square root of 2, Pythagoras constant. [4] 1.41421 35623 73095 04880 ... Continued fractions with more than 20 known terms have been truncated, ...
The latter fraction is the best possible rational approximation of π using fewer than five decimal digits in the numerator and denominator. Zu Chongzhi's results surpass the accuracy reached in Hellenistic mathematics, and would remain without improvement for close to a millennium.
Pi Approximation Day is observed on July 22 (22/7 in the day/month date format), since the fraction 22 ⁄ 7 is a common approximation of π, which is accurate to two decimal places and dates from Archimedes. [33] In Indonesia, a country that uses the DD/MM/YYYY date format, some people celebrate Pi Day every July 22. [34]
In the 1760s, Johann Heinrich Lambert was the first to prove that the number π is irrational, meaning it cannot be expressed as a fraction /, where and are both integers. In the 19th century, Charles Hermite found a proof that requires no prerequisite knowledge beyond basic calculus .
Lagrange's discovery implies that the canonical continued fraction expansion of the square root of every non-square integer is periodic and that, if the period is of length p > 1, it contains a palindromic string of length p − 1. In 1813 Gauss derived from complex-valued hypergeometric functions what is now called Gauss's continued fractions ...
Its continued fraction is A040000 in the OEIS and its decimal expansion is A002193. This number is listed in Finch's book, and it is sometimes called "Pythagoras' constant," though "square root of two" is considered manageable enough. Thus, the square root of 2 is notable enough for Wikipedia.
The area within a circle is equal to the radius multiplied by half the circumference, or A = r x C /2 = r x r x π.. Liu Hui argued: "Multiply one side of a hexagon by the radius (of its circumcircle), then multiply this by three, to yield the area of a dodecagon; if we cut a hexagon into a dodecagon, multiply its side by its radius, then again multiply by six, we get the area of a 24-gon; the ...