[Tex/LaTex] Only left brace or bar in math equations


I wanna insert only a left bar like \left | without the closing right bar.

I want to use it as separator of calculation hints.

$a * b = c | :b\\
a = \frac{c}{b}$

and so on.

It must be a left bar and not only | or \vert so that it is scaled in height.

Best Answer

A single . can be used as the partner of a bracket, e.g.:

\left| \frac{b}{c} \right.
\left. \frac{b}{c} \right|

There is also \middle in order to scale something in the middle of an expression, e.g.:

\left. a * b = c \middle| :b \right.

However, in your case, probably you should use some way to align your computation across several lines. This can be done using, for example, the environment align from package amsmath:

    a * b &= c   &&| :b\\
    a     &= \frac{c}{b}

This will, however, lead to the problem that you cannot use \left and \right across different cells of an align, as explained at https://tex.stackexchange.com/a/89621/88939.

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