gMath is an Add-on for Google Forms (and Docs, Sheets) that allows you to easily create, and insert, mathematical equations and graphs.  It uses the LaTeX equation editor to allow you to quickly use buttons, or write it all out yourself, to insert the equations or graphs into a Google Form.  With the recent update, you can quickly allow students to use gMath to submit their own answers using the equation, graph, or handwriting editor.  This Add-on makes it very easy to create graphs and equations as well as allowing students the ability to do the same.