Example of line intersection & it's dependencies.

dg.js example code

		var canvas = dg.Canvas("testcanvas", { border: "1px solid #ccc"});
		var axes = dg.Axes([canvas.width() / 4, canvas.height() / 1.5]).hide(false);
		
		var p1 = dg.Point([1,1]).label("A");
		var p2 = dg.Point([5,2]).label("B");
		
		l0 = dg.Line(p1, p2);
		
		var p3 = dg.Point([7,7]).label("C");
		var p4 = dg.Point([1,-2]).label("D");
		var l1 = dg.Line(p3, p4);
		
		var intersection = dg.Intersect(l0, l1);
		var pl = dg.PerpendicularLine(intersection, l0);
		var o = dg.Circle(intersection, p2);