A unit circle for derivation of the cosine difference formula using distance formula

						JXG.Options.axis.ticks.insertTicks = false;
JXG.Options.axis.ticks.ticksDistance = 10;
var board = JXG.JSXGraph.initBoard('box1', {
boundingbox:  [-1.3, 1.3, 1.3, -1.3],showcopyright: false,showNavigation: false,axis: true,defaultAxes: {
    y: { 
	ticks: {majorHeight: 5 },
	withLabel:true,
    name: 'Y',
      label: {
        position: 'rt',
        offset: [10, 0]
      }
	},
	x: { 
	ticks: {majorHeight: 5 },
	name: 'X',
    withLabel: true,
    label: {
        position: 'rt',
      offset: [-10, -15]
    } },
  }, 
});
 

var p1 = board.create('point', [0, 0],{name:'O',size: 1, fixed:true, label: {offset:[-15,-10], color:'blue'
}} );


var c1 = board.create('circle',[p1, 1]);

var p2 = board.create('glider', [0.76,0.65, c1],{name:"(x2,y2)",face:'',label:{offset:[5,5]}});
var p3 = board.create('glider', [-0.25,0.96, c1],{name:"(x1,y1)",face:'',label:{offset:[-20,15]}});

var l1 = board.create('segment', [p1, p2]);
var l2 = board.create('segment', [p1, p3]);
var l3 = board.create('segment', [p2, p3]);
var l4 = board.create('axis', [[0.0, 0], [1, 0]],{});
var l5 = board.create('axis', [[0.0, 0], [0, 1]]);

var pp4 = board.create('perpendicularpoint', [p2, l4],{visible:false});

a1 = board.create('angle',[pp4, p1, p3], {radius: 0.3,label:{offset:[-20,5]}});

a2 = board.create('angle',[pp4, p1, p2], {radius: 0.5});
a3 = board.create('angle',[p2, p1, p3], {radius: 0.6,name:"α - β",label:{offset:[-10,-2]}});
//alert(a3.Value())