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<big><math>\pi</math></big> ('''Pi''') is the symbol used in mathematics for the ratio of the circumference of a circle to its diameter, which turns out to be a very important number, appearing in many formulations of mathematics and physics.   

'''Pi''' is the sixteenth letter of the [[Greece|Greek]] alphabet and is used in its lower case form (<big><math>\pi</math></big>) to represent the mathematical constant of the same name which is defined as ''the ratio of the circumference of a circle to its diameter''.  It is an important number and appears in many [[mathematics|mathematical]] and [[physics|physical]] formulae.   

<big><math>\pi</math></big> is an [[irrational number]]; this means that it cannot be expressed as a fraction, and (therefore) cannot be expressed exactly as a decimal no matter how many decimal places it is carried out to.  

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 decimal places it is carried out to).  

The value of <big><math>\pi</math></big> is approximately 3.14159 in decimal. This value is precise enough for almost all ordinary purposes; it can, for example, be used to calculate the circumference of the Earth with an error of only about 110 feet.  

The value of <big><math>\pi</math></big> is approximately 3.14159 in decimal. This value is precise enough for almost all ordinary purposes; it can, for example, be used to calculate the circumference of the Earth with an error of only about 110 feet.