By default, tinyMCE editor does not support mathematical formula and equation writing. To have this functionality you need to use a third-party plugins, WIRIS
Just download a package of WIRIS editor from this URL for php platform.
By default, TinyMCE in Joomla! 3.0 will not accept any html entity, like <strong>, <div> etc. This is happen because this editor strips html entity by default upon saving. You can solve this issue by changing its default configuration as bellow: