title: Why does .NET Math.Cos() return a wrong answer for pi/2?
body: <p>I have a method to convert degrees to radians...</p>
  
  <pre><code>public static double ToRadians(double degAngle) 
  {
      return Math.PI * degAngle / 180;
  }
  </code></pre>
  
  <p>...and it works pretty well.
  But when I try 
  <code>Math.Cos(ToRadians(90));</code>, it returns 6.12303176911189E-17. Why does this happen? </p>