WP LaTeX is installed and enabled for comments. You may read more about how to use this plugin here.

The input

`[latex]e^{\i \pi} + 1 = 0[/latex]`

is rendered by the plugin as

The input

`[latex]R=\frac{\displaystyle{\sum_{i=1}^n (x_i-\bar{x})(y_i- \bar{y})}}{\displaystyle{\left[ \sum_{i=1}^n(x_i-\bar{x})^2 \sum_{i=1}^n(y_i-\bar{y})^2 \right]^{1/2}}}[/latex]`

turns to

Note that there should not be any line breaks in the LaTeX code you place between the [latex] and [/latex] tags.