public static Point2double ReflectPoint(this Line2double l, Point2double p)
{
var m = l.Slope();
var c = l.YIntercept();
var d = (p.X + (p.Y - c) * m) / (1 + m * m);
var x = 2 * d - p.X;
var y = 2 * d * m - p.Y + 2 * c;
return(new(x, y));
}
