## Labels Used in Algebra

There are many symbols and letters used in algebra, and many of them have a special meaning.
$\pi$
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.