load (draw);

a : [0.8, 2.5];
b : [2, 1.0];

beta  : atan (b[2] / b[1]);
alpha : atan (a[2] / a[1]);
delta : alpha - beta;

lsg1 : solve (
    [
      a[1] + r*b[2] = s * b[1], 
      a[2] - r*b[1] = s * b[2]
    ], [r, s]);
rs : rhs (lsg1[1][1]);
Hb : rs * b;

draw2d (
  xrange = [0, 3.7],
  yrange = [0, 3.7],
  /* */
  head_length = 0.1,
  vector ([0, 0], a),
  vector ([0, 0], b),
  vector (a, b),
  vector (b, a),
  /* Winkel eintragen */
  transparent = true,
  ellipse (0, 0, 0.2, 0.2, 360*beta / (2*%pi), 360*delta / (2*%pi)),
  /* */
  points_joined = true,
  point_size = 0.05,
  points ([a, Hb]),
  /* */
  xtics = false,
  ytics = false,
  user_preamble = [
                "set noborder",
                "set label '{/Symbol g}' at 0.08, 0.13 center",
                "set label '{/=25 @_{/=25 a}^{/=15 ->}}' at 0.3, 1.6",
                "set label '{/=25 @_{/=25 b}^{/=12 ->}}' at 0.8, 0.3",
                "set label '{/=25 |a|sin({/Symbol g})}' at 1.3, 1.8",
                "set size square"
                ],
  /* */
  dimensions = [800, 800],
  file_name = "herleitungFlaecheSchritt02Parallelogramm",
  terminal = eps
);