Slider and function plot

The code to produce this page

var brd = JXG.JSXGraph.initBoard('jxgbox', {boundingbox: [-10, 10, 10, -10], axis:true}),
    a = brd.create('slider',[[2,-5],[7,-5],[-5,1,5]], {name:'a'}),
    b = brd.create('slider',[[2,-6],[7,-6],[-5,0,5]], {name:'b'}),
    c = brd.create('slider',[[2,-7],[7,-7],[-5,0,5]], {name:'c'}),

    f = brd.create('functiongraph',[function(x){
            return a.Value()*x*x + b.Value()*x + c.Value();
        }]);