Polygon II

The triangle ABC can be moved around by dragging A and it can be rotated around A by moving B.

The underlying JavvaScript code

For the elements c1, p3, line the attribute visible should be set to false.

var brd = JXG.JSXGraph.initBoard('jxgbox',{boundingbox:[-3,3,3,-3]});
var p1 = brd.create('point',[-1,-1]);

var c1 = brd.create('circle',[p1,3],{strokeOpacity:0.1});      // 
var p2 = brd.create('glider',[2,-1,c1]);                       // p2 glides on circle c1

var rot = brd.create('transform',[function(){ return Math.PI/4;},p1],{type:'rotate'});  // rot is defined by the angle BAC
var p3 = brd.create('point',[p2,rot],{fixed:true,size:1,name:'h1'});                    // h1: B rotated around A with angle rot
var line = brd.create('line',[p1,p3],{strokeOpacity:0.1});                              // line through A and h1

var p4 = brd.create('glider',[0,0.5,line],{fixed:true});                                // C is on the line with a fixed distance from A
var poly = brd.create('polygon',[p1,p2,p4], {fillOpacity:0.05});