Area of a trangle formula by base and height

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

var p1 = board.create('point', [-7, 0],{name:'',face:''});
var p2 = board.create('point', [1.5, 7.5],{name:'',face:''});
var p3 = board.create('point', [6, 0],{name:'',face:'',});
var l1 = board.create('segment', [p1, p2]);
var l2 = board.create('segment', [p2,p3],);
var l3 = board.create('segment', [p1, p3],{withlabel:true,name:'b',label:{offset:[0,-10]}});
var perp1 = board.create('perpendicularsegment', [l3,p2],{withlabel:true,name:'h',color:'blue',label:{offset:[-15,-60],color:'blue'}});

var pl1 = board.create('parallel', [l2, p1],{visible:false});
var pl2 = board.create('parallel', [l1, p3],{visible:false});
var i1 = board.create('intersection', [pl1, pl2],{name:'',face:''});
var l4 = board.create('segment', [i1,p3],{dash:2});
var l5 = board.create('segment', [i1,p1],{dash:2});