Labels Used in Algebra
\[\pi\]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
\[y\], as are coordinate axes, though other symbols can be used.
Integers are generally labelled
\[n\](the 'natural numbers' are the positive integers) and
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.