JXG Preview

<div id="bkmrk-jxgbox" class="jxgbox" style="margin:auto;width:300px; height:300px;"></div>
<script>
JXG.Options.label.autoPosition = true;
JXG.Options.text.fontSize = 24;
var board = JXG.JSXGraph.initBoard("bkmrk-jxgbox", {boundingbox: [-5,5,5,-5], axis:false, showCopyright:false, showNavigation:false});
var a = board.create('point', [-4, 0], {name:'$a$'});
var b = board.create('point', [4, -3], {name:'$b$'});
var c = board.create('point', [1, 4], {name:'$c$'});
var s1 = board.create('segment', [a, b], {color: 'black'});
var s2 = board.create('segment', [a, c], {color: 'black'});
var s3 = board.create('segment', [c, b], {color: 'black'});
var as = board.create('glider', [3, 0, s3], {name:"$a'$"});
var bs = board.create('glider', [4, -3, s2], {name:"$b'$"});
var cs = board.create('glider', [1, 4, s1], {name:"$c'$"});
var s4 = board.create('segment', [a, as], {color: 'black'});
var s5 = board.create('segment', [b, bs], {color: 'black'});
var s6 = board.create('segment', [c, cs], {color: 'black'});
var txt = board.create('text', [-4.5, -4, "$\\alpha$"],{parse:false});
</script>