Click the Symbols item on the toolbar to open the symbol table dropdown. This shows a large list of Mathemtical sybols that can be inserted in your document by clicking on them.

osx-symbols-table

You can scroll through the entire list, but these symbols are grouped by type, click on a heading to scroll to that group.

Some symbols names are larger than can be displayed, hover over the symbol and the full title will be shown in the tooltip.