Quelltext der Konstruktion

  board = JXG.JSXGraph.initBoard('jxgbox', {boundingbox:[-4, 6, 8, -4], axis: true, grid: false,
                                 keepaspectratio: true, showcopyright: false});
  p1 = board.createElement('point', [0, 0]);
  p2 = board.createElement('point', [6, 0]);
  p3 = board.createElement('point', [4, 4]);

  t1 = board.createElement('triangle', [p1, p2, p3], {strokeWidth: '1px'});

  m1 = board.createElement('point', [4, 1.5], {style:2,name:"X"});

  l1 = board.createElement('perpendicularpoint', [m1, t1.c]);
  l2 = board.createElement('perpendicularpoint', [m1, t1.a]);
  l3 = board.createElement('perpendicularpoint', [m1, t1.b]);

  t2 = board.createElement('triangle', [l1, l2, l3], {strokeWidth: '1px'});

  // Get area of triangle given by the three points A, B, C
  getTriangleArea = function(A, B, C, square) {
    var a = B.coords.distance(JXG.COORDS_BY_USER, C.coords),
        b = A.coords.distance(JXG.COORDS_BY_USER, C.coords),
        c = B.coords.distance(JXG.COORDS_BY_USER, A.coords),
        s = (typeof square == 'undefined' ? true : square);

    if (s)
      return (4*a*a*c*c-(a*a+c*c-b*b)*(a*a+c*c-b*b));
    else
      return Math.sqrt((4*a*a*c*c-(a*a+c*c-b*b)*(a*a+c*c-b*b))/16.);
  };

  te = board.createElement('text', [-3.8, 5.5, function () { return ("Fläche des Dreiecks EDF: " + getTriangleArea(l1, l2, l3, false)); }]);

  // dependency and polynomial generation hacking
  m1.ancestors[l1.id] = l1;
  m1.ancestors[l2.id] = l2;
  m1.ancestors[l3.id] = l3;
  m1.ancestors[p1.id] = p1;
  m1.ancestors[p2.id] = p2;
  m1.ancestors[p3.id] = p3;

  m1.generatePolynomial = function () {
    var as16 = getTriangleArea(l1, l2, l3),
        as = '((('+l2.symbolic.x+')-('+l3.symbolic.x+'))^2+(('+l2.symbolic.y+')-('+l3.symbolic.y+'))^2)',
        bs = '((('+l1.symbolic.x+')-('+l3.symbolic.x+'))^2+(('+l1.symbolic.y+')-('+l3.symbolic.y+'))^2)',
        cs = '((('+l2.symbolic.x+')-('+l1.symbolic.x+'))^2+(('+l2.symbolic.y+')-('+l1.symbolic.y+'))^2)',
        poly = '4*'+as+'*'+cs+'-('+as+'+'+cs+'-'+bs+')*('+as+'+'+cs+'-'+bs+')-('+as16+')';

    return ['4*'+as+'*'+cs+'-('+as+'+'+cs+'-'+bs+')*('+as+'+'+cs+'-'+bs+')-('+as16+')'];
  };

  loc = board.createElement('locus', [m1], {strokeColor: 'red', strokeWidth: '1px'});

  createControlElements = function () {
    glider = board.createElement('glider', [0, 5, loc]);
    lg1 = board.createElement('perpendicularpoint', [glider, t1.a]);
    lg2 = board.createElement('perpendicularpoint', [glider, t1.b]);
    lg3 = board.createElement('perpendicularpoint', [glider, t1.c]);

    tecontrol = board.createElement('text', [-3.8, 5, function () { return ("Fläche des Dreiecks HIJ: " + getTriangleArea(lg1, lg2, lg3, false)); }]);
  }