PYTHAGOREAN CONSTANT: The square root of 2 , often known as root 2 , radical 2 , or Pythagoras' constant , and written as √ 2 , is the positive algebraic number that, when multiplied by itself, gives the number 2 . It is more precisely called the principal square root of 2 , to distinguish it from the negative number with the same property. ARCHIMEDES'S CONSTANT: The constant π (pi) has a natural definition in Euclidean geometry as the ratio between the circumference and diameter of a circle. It may be found in many other places in mathematics: for example, the Gaussian integral , the complex roots of unity , and Cauchy distributions in probability .