Area of a trangleby Heron’s formula

						var board = JXG.JSXGraph.initBoard('box1', {
boundingbox: [-10, 9, 10, -11],showNavigation:false, showcopyright: false, axis: false,
});

var p1 = board.create('point', [-7, 0],{face:'',name:''});
var p2 = board.create('point', [1.5, 7.5],{face:'',name:''});
var p3 = board.create('point', [6, 0],{face:'',name:''});
var l1 = board.create('segment', [p1, p2],{withlabel:true,name:'c',label:{offset:[-10,10]}});
var l2 = board.create('segment', [p2,p3],{withlabel:true,name:'a',label:{offset:[10,0]}});
var l3 = board.create('segment', [p1, p3],{withlabel:true,name:'b',label:{offset:[0,-10]}});