title: Angle between two Vectors 2D
body: <p>I'm trying to compute the angle between two vectors.
  I tried this, but it always returns zero:</p>
  <pre><code>public double GetAngle(Vector2 a, Vector2 b)
  {
      double angle = Math.Atan2(b.Y, b.X) - Math.Atan2(a.Y, a.X);
      return angle;
  }
  
  GetAngle(new Vector2(1,1), new Vector2(50,50));
  </code></pre>
  <p><a href="https://i.stack.imgur.com/sVPA2.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sVPA2.png" alt="Vectors" /></a><a href="https://i.stack.imgur.com/77Mf3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/77Mf3.png" alt="The angle I need" /></a></p>