I was wanting to know of a useful way to create large `\left\langle`

and `\right\rangle`

commands. I have tried all up-sizing commands but get a message that they cannot be used in math mode. Such as:

```
\large
\Large
\LARGE
\huge
```

Also I have tried, `\left\left\langle...\right\right\rangle`

to no working either.

MWE:

```
\documentclass[11pt,a5paper]{article}
\usepackage{amsmath}
\def\P{\mathbf{P}}
\def\Q{\mathbf{Q}}
\def\la{\left\langle}
\def\ra{\right\rangle}
\begin{document}
\begin{align*}
\P-\Q \;&=\; \large\la (1-(-2)), (2-1), (-1-3) \large\ra \
\;&=\; \la 3, 1, -4 \ra. \
\\
|\P-\Q| \;&=\; \sqrt{x^2+y^2+z^2} \\
\;&=\; \sqrt{(3)^2 + (1)^2 + (-4)^2} \\
\;&=\; \sqrt{9+1+16} \\
\;&=\; \sqrt{26}
\end{align*}
\end{document}
```

## Best Answer

As you've discovered, the fontsize-changing commands

`\large`

,`\Large`

,`\huge`

, and`\Huge`

work only in text mode. Different commands are required for math mode.In math mode, the easiest way to change the height/depth of "fences" -- such as round parentheses, square brackets, curly braces, angle brackets, and many other such delimiters -- is to prefix them with

`\left`

and`\right`

commands, respectively. The height of the fences will be setautomatically: the fences will be at least as tall as the math material they enclose. A side benefit of using the`\left ...`

\right`method is that it provides some useful syntax checking: LaTeX will issue an error message if it cannot match every`

\left`statement to a`

\right` statement, and vice versa.If you want direct control over the size of the fences, you can prefix the fence symbols -- in order of increasing size -- with

`\big`

,`\Big`

,`\bigg`

, and`\Bigg`

. If you use these statements in pairs, such as`\biggl[`

and`\biggr]`

, LaTeX will perform some syntax checking for you.The

downsideof having such direct control over the size of the fences is that you need to know -- either in advance, or by trial and error -- which size to choose.One

upsideto having direct control over the size of the fences is that -- as you've also discovered -- the`\left ... \right`

mechanism does not always get the job done. E.g., in the snippetthe outer parentheses will have the exact same size as the inner ones, which is probably not what you're trying to achieve. In such a case, you need to type

in order to enlarge the outer set of parentheses a bit.

A second instance where having direct control over the size of the fences is desirable is the case

because the size of the parentheses generated by the

`\left ... \right`

method would be too large, typographically speaking.A third reason for not using the

`\left ... \right`

method is that it adds some potentially unwanted whitespace around the fences. One way to avoid this problem is to load the mleftright package and to use the commands`\mleft`

and`\mright`

instead of`\left`

and`\right`

. (If you're sure you'llalwayswant to suppress the extra amount of whitespace generated by the`\left`

and`\right`

commands, you could load the`mleftright`

package and issue the instruction`\mleftright`

in the preamble; doing so will redefine`\left`

and`\right`

to act like`\mleft`

and`\mright`

, respectively.)For more information on the whitespace issues created by

`\left`

and`\right`

and how to deal with them, you may want to check out the question Spacing around \left and \right.That said, most of the time you'll be just fine if you use the

`\left ... \right`

method. Happy TeXing!