A line bisects an interanl angle of a right triangle with an altitude from intersection point

						var board = JXG.JSXGraph.initBoard('box1', {
axis: true, boundingbox: [-15, 15, 15, -15], showcopyright: false,keepaspectratio: true, axis: false, zoom: false,showNavigation: false
  });
var p1 = board.create('point', [-10, 4],{name:'A', size: 1,face:"", color:'blue', fixed: true,label: {offset:[-15,-10], color:'blue'}} );  
var p2 = board.create('point', [5, 12.66],{name:'B', size: 1,face:"", color:'blue', fixed: true,label: {offset:[-5,10], color:'blue'}} );
var p3 = board.create('point', [5, 4],{name:'C', size: 1,face:"", color:'blue', fixed: true,label: {offset:[-5,-10], color:'blue'}} );

var l1 = board.create('segment', [p1, p2]);
var l2 = board.create('segment', [p2, p3]);
var l3 = board.create('segment', [p1, p3]);

var bi1 = board.create('bisector', [p2, p1, p3],{visible:false});

var i1 = board.create('intersection', [l2, bi1],{name:'D', face:"",  label: {offset:[5,0], color:'blue'}} );
var l4 = board.create('segment', [p1, i1]);

var perp1 = board.create('perpendicularsegment', [l1, i1],{dash:2,color:'blue'});

var i1 = board.create('intersection', [l1, perp1],{name:'E', face:"",  label: {offset:[-10,10], color:'blue'}} );