public bool Equals(Vector2D v)
{
if ((object)v == null)
{
return false;
}
return this.x == v.x && this.y == v.y;
}
public static Vector2D Rotate(Vector2D v, double a)
{
double x = Math.Cos(a) * v.x - Math.Sin(a) * v.y;
double y = Math.Sin(a) * v.x + Math.Cos(a) * v.y;
return new Vector2D(x, y);
}