Changes

'''Pi''' (<big><math>\pi</math></big>) is the ratio of the circumference of a circle to its diameter.  The value of <big><math>\pi</math></big> is an [[irrational number]]; which means that it cannot be fully expressed as a fraction or a decimal (regardless of the number of digits used). To five decimal places, <big><math>\pi</math></big> <big><math>\approx</math></big> 3.14159.  Using the convention that Greek letters in mathematics have conventional meaning, the ratio takes its name from the sixteenth letter of the [[Greek alphabet]].  It is an important number and appears in many [[mathematical]] and [[physics|physical]] formulae.   

'''Pi''' (<big><math>\pi</math></big>) is the ratio of the circumference of a circle to its diameter.  The value of <big><math>\pi</math></big> is both an [[irrational number]] and a [[transcendental number]]; which means that it cannot be fully expressed as a fraction or a decimal (regardless of the number of digits used), nor can it be expressed as the solution to any polynomial equation with rational coefficients. To five decimal places, <big><math>\pi</math></big> <big><math>\approx</math></big> 3.14159.  Using the convention that Greek letters in mathematics have conventional meaning, the ratio takes its name from the sixteenth letter of the [[Greek alphabet]].  It is an important number and appears in many [[mathematical]] and [[physics|physical]] formulae.   

The approximate value of 3.14159 is precise enough for almost all ordinary purposes; it can, for example, be used to calculate the circumference of a circle of the size of the Earth with an error of only about 110 feet. For rough approximations, the fraction 22/7 (= 3.142857...) is sometimes used.

The approximate value of 3.14159 is precise enough for almost all ordinary purposes; it can, for example, be used to calculate the circumference of a circle of the size of the Earth with an error of only about 110 feet. For rough approximations, the fraction 22/7 (= 3.142857...), accurate to 2 decimal places, is sometimes used.  A more accurate fractional approximation is 355 / 113 (= 3.14159292), which is accurate to 6 decimal places.

==History==

==History==