\[\pi\]
is a very special number, special enough to have a symbol to label it.Less special numbers have letters to label them. Unknown numbers are labelled
\[x\]
or \[y\]
, as are coordinate axes, though other symbols can be used.Integers are generally labelled
\[n\]
(the 'natural numbers' are the positive integers) and \[m\]
.Lengths can be labelled by lots of different letter:
\[a, \: b, \: c\]
are used for triangles, \[a, \: b, \: h\]
are used for trapeziums, and \[r\]
is used for the radius of a circle. \[l\]
is used to label the length of an arc - part of the perimeter - of a circle, and \[s\]
is used to lbel the slant height of a cone.