title: Math.Atan2 yields strange result?
body: <p>First, my math is not strong! But I was calculating the angle of a point from the origin (0, 0) to (-1, -1).</p>
  
  <p>This angle is 225° or 5π/4.</p>
  
  <ul>
  <li>5π/4 = 3.9269908169872415480783042290994</li>
  <li>Math.Atan2(-1, -1) = -2.3561944901923448</li>
  </ul>
  
  <p>Perhaps my understanding of <code>Math.Atan2</code> is incorrect but I thought it was meant to return the degree of an angle given two points on a circle whose origin is (0, 0). What I assume is happening here is that the result from <code>Atan2</code> is "flipped" since it is on the negative side of the X axis...can someone confirm and provide the proper way to do this?</p>
  
  <p>This is my test, which fails:</p>
  
  <pre><code>Assert.AreEqual((5 * Math.PI) / 4, Math.Atan2(-1, -1));
  </code></pre>
  
  <p>And here's my <code>PointD</code> class which holds points X and Y:</p>
  
  <pre><code>public double ToRadians()
  {
      double radians = Math.Atan2(this.Y, this.X);
  
      return radians;
  }
  </code></pre>