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'''Pi''' is the sixteenth letter of the [[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 [[mathematical]] and [[physics|physical]] formulae.   

'''Pi''' is the sixteenth letter of the [[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 [[mathematical]] and [[physics|physical]] formulae.   

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).  

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).