Writing basic formulas

LaTeX offers three writing modes:

• Paragraph mode: The text is typeset as a sequence of words in lines, paragraphs, and pages. That's what we used in the previous chapters.
• Left-to-right mode: The text is a sequence of words, but LaTeX typesets it from left to right without breaking the line. For instance, the argument of \mbox will be typeset in this mode; so \mbox prevents hyphenation.
• Math mode: Here, LaTeX treats letters as math symbols. That's why they're typeset in italics, which is common practice for variables. A lot of symbols can only be used in math mode. Such symbols are roots, sum signs, relation signs, math accents, arrows, and various delimiters, such as brackets and braces. LaTeX ignores space characters between letters and symbols. Instead, the spacing depends on the type of symbols—spacing of relation signs is different from spacing of opening or closing delimiters. All math expressions require this mode...