TeX and MathJax are not clairvoyant. If you tell them to typeset one fraction, they happily comply. But one fraction will have just one fraction line.

Your formula should be typeset as three separated fractions:

```
\frac{1}{2} \frac{eV}{md} \frac{x^{2}}{v^{2}}
```

or, maybe better,

```
\frac{1}{2} \, \frac{eV}{md} \, \frac{x^{2}}{v^{2}}
```

(spaces are optional, but make for good reading).

This is a MathJax rendering of the same:

but remember this is browser and machine dependent.

Using `{1\over 2}`

is deprecated in LaTeX, so, unless you use Plain TeX for your documents, it's better to use `\frac`

also in MathJax. There would be no advantage with it, because `\over`

makes just one fraction line, just like `\frac`

.

## Best Answer

Here's a LaTeX-based solution. The macro

`\mychoose`

should be used only in "text-style" math mode. (I trust it's not too difficult to adapt it to MathJax.)Addendum: If you want square brackets instead of round parentheses, simply adjust the code in the`\mychoose`

macro.