If either the MathJax or the TeX filters are enabled (in Site administration > Plugins > Filters > Manage filters) then the Insert equation option is provided in the TinyMCE editor for launching the equation editor.
If either the MathJax or the TeX filters are enabled (in Site administration > Plugins > Filters > Manage filters) then the Insert equation option is provided in the TinyMCE editor for launching the equation editor.