>"$" ("$$" to be exact) is actually used in TeX to indicate opening and closing of statements/mathematical expressions. Both are used. A single $ is used for i

>"$" ("$$" to be exact) is actually used in TeX to indicate opening and closing of statements/mathematical expressions. Both are used. A single $ is used for inline math, the double $$ begins an equation on its own line. For example: The solution to $ax^2 + bx + c = 0$ will be $$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$ The first block will be mid-sentence, while the second one will get its own line.