Barycenter

The underlying JavaScript code

JXG.Options.label.autoPosition = true;
JXG.Options.text.fontSize = 20;

var board = JXG.JSXGraph.initBoard("jxgbox", {boundingbox: [-2,7,7,-2], axis: true, showCopyright:false, showNavigation:false});

var p0  = board.create('point', [0, 0], {name:"p_0"});
var p0s = board.create('point', [2, 1], {name:"p_0'"});
var p1s = board.create('point', [4, 4], {name:"p_1'"});
var p2s = board.create('point', [1, 2], {name:"p_2'"});

var l1 = board.create('line', [p0s, p1s], {lastArrow: true, color: 'orange'});
var l2 = board.create('line', [p0s, p2s], {lastArrow: true, color: 'orange'});
var v1 = board.create('arrow', [p0s, p1s], {color: 'black', strokeWidth: 1, layer: 8, lastArrow:{size: 10}});
var v2 = board.create('arrow', [p0s, p2s], {color: 'black', strokeWidth: 1, layer: 8, lastArrow:{size: 10}});

var v3 = board.create('arrow', [p0, p0s], {color: 'black', strokeWidth: 1, layer: 8, lastArrow:{size: 10}});

var q = board.create('point', [3, 5], {name:"q"});

var par1 = board.create('parallel', [l1, q], {strokeWidth: 1, dash: 1});
var par2 = board.create('parallel', [l2, q], {strokeWidth: 1, dash: 1});