Trinket is really handy

If you know a bit of Python (or even if you don’t and you are prepared to copy and modify other users’ code) then you can graph formulae, create an embed code and share the result online.
Best of all you don’t have to fork out any hard earned to get started.
For example: here is my embed code for a graph showing impact speed vs height for objects in free-fall near the earth’s surface:
<iframe src="" width="100%" height="600" frameborder="0" marginwidth="0" marginheight="0" allowfullscreen></iframe>and when you add that code to your site you get this: