Consider any circle of diameter #(D)# and circumfenence #(C)#

Then #pi = C/D# It can be proved that #pi# is a constant for any circle.

#pi approx 3.14159265# (to 8 decimal places)

#pi# is irrational (i.e. cannot be expressed as a fraction: #p/q :p,q in ZZ#)

#pi# is also transcendental (i.e. is not the root of any polynomial equation with rational coefficients)

#pi# is one of the most common real constants in all of mathematics.