Sage Math Tutorial - Fourier Series (Interactive!)

Demoed below is an awesome Sage featured called an 'Interact'. It has the same edit-and-evaluate features of a regular Sage Cell, plus interactive sliders, drop-downs, and buttons that allow the user to modify parameters on-the-fly. Also note that I have hidden the input box and the evaluate button, and that I have set the Cell to automatically evaluate when the page is loaded; almost everything about a Cell can be customized in the page's CSS. Play!