<iframe 
    src="https://www.jsxgraph.uni-bayreuth.de/share/iframe/thales-inscribed-angle-theorem" 
    style="border: 1px solid black; overflow: hidden; width: 550px; aspect-ratio: 55 / 65;" 
    name="JSXGraph example: Thales' inscribed angle theorem" 
    allowfullscreen
></iframe>

<div id="board-0-wrapper" class="jxgbox-wrapper " style="width: 100%; ">
   <div id="board-0" class="jxgbox" style="aspect-ratio: 1 / 1; width: 100%;" data-ar="1 / 1"></div>
</div>

<script type = "text/javascript"> 
    /*
    This example is licensed under a 
    Creative Commons Attribution ShareAlike 4.0 International License.
    https://creativecommons.org/licenses/by-sa/4.0/
    
    Please note you have to mention 
    The Center of Mobile Learning with Digital Technology
    in the credits.
    */
    
    const BOARDID = 'board-0';

    var board = JXG.JSXGraph.initBoard(BOARDID, { boundingbox: [-6, 6, 6, -6], keepaspectratio: true });
    var o = board.create('point', [0, 0], { name: 'O' });
    var c = board.create('circle', [o, 4], { name: 'C' });
    
    var a = board.create('glider', [3, 0, c], { name: 'A' });
    var b = board.create('glider', [-3, -3, c], { name: 'B', label: { offset: [-15, 0] } });
    var p = board.create('point', [-1, 2], { name: 'P' });
    
    var opts = { strokeColor: 'blue' };
    var lab = board.create('segment', [a, b], opts);
    
    var lpb = board.create('segment', [p, b], opts);
    var lpa = board.create('segment', [a, p], opts);
    
    var op = board.create('line', [o, p], { visible: false });
    
    var pp = board.create('intersection', [c, op, 0], { name: 'P\'', label: { offset: [0, 15] } });
    var opts = { strokeColor: 'green' };
    var lppb = board.create('segment', [pp, b], opts);
    var lppa = board.create('segment', [a, pp], opts);
    var opts = { strokeColor: 'lightblue', strokeWidth: '1px' };
    var lopp = board.create('segment', [o, pp], opts);
    
    var angp = board.create('angle', [b, p, a]);
    var angpp = board.create('angle', [b, pp, a]);
    
    var label_p = board.create('smartlabel', [angp], {digits: 1, unit: '°', useMathJax: false});
    
 </script> 

<jsxgraph width="100%" aspect-ratio="1 / 1" title="Thales' inscribed angle theorem" description="This construction was copied from JSXGraph examples database: BTW HERE SHOULD BE A GENERATED LINKuseGlobalJS="false">
   /*
   This example is licensed under a 
   Creative Commons Attribution ShareAlike 4.0 International License.
   https://creativecommons.org/licenses/by-sa/4.0/
   
   Please note you have to mention 
   The Center of Mobile Learning with Digital Technology
   in the credits.
   */
   
   var board = JXG.JSXGraph.initBoard(BOARDID, { boundingbox: [-6, 6, 6, -6], keepaspectratio: true });
   var o = board.create('point', [0, 0], { name: 'O' });
   var c = board.create('circle', [o, 4], { name: 'C' });
   
   var a = board.create('glider', [3, 0, c], { name: 'A' });
   var b = board.create('glider', [-3, -3, c], { name: 'B', label: { offset: [-15, 0] } });
   var p = board.create('point', [-1, 2], { name: 'P' });
   
   var opts = { strokeColor: 'blue' };
   var lab = board.create('segment', [a, b], opts);
   
   var lpb = board.create('segment', [p, b], opts);
   var lpa = board.create('segment', [a, p], opts);
   
   var op = board.create('line', [o, p], { visible: false });
   
   var pp = board.create('intersection', [c, op, 0], { name: 'P\'', label: { offset: [0, 15] } });
   var opts = { strokeColor: 'green' };
   var lppb = board.create('segment', [pp, b], opts);
   var lppa = board.create('segment', [a, pp], opts);
   var opts = { strokeColor: 'lightblue', strokeWidth: '1px' };
   var lopp = board.create('segment', [o, pp], opts);
   
   var angp = board.create('angle', [b, p, a]);
   var angpp = board.create('angle', [b, pp, a]);
   
   var label_p = board.create('smartlabel', [angp], {digits: 1, unit: '°', useMathJax: false});
   
</jsxgraph>