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copied!<p>Basically, it looks like this is expected behavior from <code>Math.Tan</code>. I don't know other languages very well, so I'm not sure if this is normal for floating point Math or specific to the C# implementation. (NOTE: Afterwards, I found that Google's online calculator returns the same suggesting it expected behavior for floating point trig functions, probably related to the fact that <em>pi</em> is irrational and the limitations of the double precision data type)</p> <p>However, working backwards from this result I am seeing that <code>Math.Atan(// your result);</code> and <code>Math.Atan(double.PositiveInfinity)</code> both return 90 degrees, suggesting this is expected?</p> <p>Here's my test:</p> <pre><code>var deg = 90.0; var rads = deg * (Math.PI / 180); var result = Math.Tan(rads); if (Double.IsInfinity(result)) Console.WriteLine("Tan of 90 degrees is Infinity"); else if (Double.IsNaN(result)) Console.WriteLine("Tan of 90 degrees is Undefined"); else Console.WriteLine("Tan of 90 degrees is {0}", result); Console.WriteLine("Arc Tan of {0} is {1} degrees", double.PositiveInfinity, Math.Atan(double.PositiveInfinity) * 180 / Math.PI); Console.WriteLine("Arc Tan of {0} is {1} degrees", result, Math.Atan(result) * 180 / Math.PI); </code></pre> <p>Which gives the output of:</p> <pre><code>Tan of 90 degrees is 1.63317787283838E+16 Arc Tan of Infinity is 90 degrees Arc Tan of 1.63317787283838E+16 is 90 degrees </code></pre> <p>So my guess is unless someone can come in and provide a workaround, you might have to program around this as an edge case to get the correct result.</p> <p>The "correct result" for any of the trig functions will be limited to the precision of <code>double</code>, which is 15 significant figures, so if you need more than that, you will need to find a library that supports more precise mathematics.</p> <p>Since <code>Math.Tan(Math.PI/2)</code> seems to provide an undesirable response you could do something like this:</p> <pre><code>public double ComputeTangent(double angleRads) { if (angleRads == Math.PI/2) return double.PositiveInfinity if (angleRads == - Math.PI/2) return double.NegativeInfinity return Math.Tan(angleRads); } </code></pre>

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