Find Quadratic Function Given its Graph - HTML5 applet
This html5 applet help you generate graphs of quadratic functions of the form $f(x)=a x^2 + b x + c$ by clicking on "Plot" (you may have to click several times to have a useful graph.). Given the graph, find coefficients $a$, $b$ and $c$ then click on "Show" to obtain the answer and "Hide" to hide the answer. Each time you click on "Plot" you get a new graph and therefore you can create as many graphs with their answers as you wish.