A right angle by intersection of two perpendicular lines

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

var p1 = board.create('point', [-3.5, -2.0],{name:'',face:''});
var p2 = board.create('point', [3.5, -2.0],{name:'',face:''});
var l1 = board.create('line', [p1,p2]);
var p3 = board.create('point', [-5, 5.0],{name:'',face:''},{name:'',face:''});

var pp1 = board.create('perpendicularpoint', [p3, l1],{name:'',face:''});

var l2 = board.create('line', [p3,pp1]);
var a1 = board.create('angle', [p1, pp1, p3],{radius:2,name:"90°",label:{offset:[3,12]}});