One of the main advantages of using L^{A}TEX is that it so good at typesetting
mathematics. Mathematical input in L^{A}TEX is typed in what is called
*math mode*. To type math that is to appear as part of a paragraph
or other piece of text, enclose the math input between a pair of dollar signs,
such as `$x<y$`

. If you use a pair of double dollar signs,
`$$x<y$$`

, you get *display math mode* where the mathematics
is displayed on a line by itself and centered horizontally on the page.
A careful mathematical typist will use math mode even for a thing
as simple as a one-character variable. This is because a variable such
as should properly be printed in italics. Math mode will take care
of this. This means that you should type the variable as `$x$`

rather
than simply as `x`

.

David Eck 2003-10-21