Riemann sums
From JSXGraph Wiki
The underlying JavaScript code
<jsxgraph width="800" height="400" box="box">
var brd = JXG.JSXGraph.initBoard('box', {axis:true, originX: 400, originY: 200, grid:true, unitX: 50, unitY: 50});
var s = brd.createElement('slider',[[1,3],[5,3],[1,10,50]],{name:'n'});
var a = brd.createElement('slider',[[1,2],[5,2],[-10,0,0]],{name:'start'});
var b = brd.createElement('slider',[[1,1],[5,1],[0,Math.PI,10]],{name:'end'});
var f = function(x){ return Math.sin(x); }
var plot = brd.createElement('functiongraph',[f,function(){return a.Value();}, function(){return b.Value();}]);
var os = brd.createElement('riemannsum',[f,
function(){ return s.Value();}, function(){ return $('sumtype').value;},
function(){return a.Value();},
function(){return b.Value();}
],
{fillColor:'#ffff00', fillOpacity:0.3});
brd.createElement('text',[-6,-3,function(){ return 'Sum='+(brd.riemannsum(f,s.Value(),$('sumtype').value,a.Value(),b.Value())).toFixed(4); }]);
</jsxgraph>