SPIP allows you to insert mathematical formulae using LaTeX notation, which will be automatically converted into an image inserted into the text.
You surround your mathematical "text" inside the <math> and </math> tags. The LaTeX code for a formula will be placed between two "$" dollar signs.
In this way, the text:
<math>the formula $a = \sqrt{b^{2} + c^{2}}$ is a reformulation of Pythagorus' formula: $a^{2} = b^{2} + c^{2}$</math>
will be displayed as:
the formula is a reformulation of Pythagorus’ formula:
An article in the documentation explains this functionality in greater depth.