MathJax: Displaying math notation on your page
The JavaScript display engine MathJax allows you to display beautiful and accessible math in all browsers. MathJax is available when you see the full text editing toolbar.
To put mathematics in a text area, you can use TeX and LaTeX notation, MathML notation, AsciiMath notation, or a combination of all three. For example, you can add the math to a Text Area like this:

and it will display on the page like this:
When \(a \ne 0\), there are two solutions to \(ax^2 + bx + c = 0\) and they are $$x = {-b \pm \sqrt{b^2-4ac} \over 2a}.$$
Learn more about using TeX or LaTeX.
Important Note
Avoid placing math content in anything other than a Text Area. Math inserted as page titles, headings, form field labels or other elements with their own semantic meaning may have unpredictable results when it comes to accessibility and compatibility with assistive technology.
Related Topics

Text Editing Toolbar
Learn more about the text editing toolbar
Do more with the text editor
Along with accessing various styles through the toolbar, you can add and edit HTML directly.