Math.Cos & Math.Sin in C#

c# trigonometry
elaverick picture elaverick · May 21, 2011 · Viewed 19.2k times · Source

I'm trying something that I thought should be reasonably simple. I have an angle, a position and a distance and I want to find the X,Y co-ordinates from this information.

With an example input of 90 degrees I convert the value to radians with the following code:

public double DegreeToRadian(float angle)
{
  return Math.PI * angle / 180.0;
}

This gives me 1.5707963267949 radians Then when I use

Math.Cos(radians)

I end up with an an answer of: 6.12303176911189E-17

What the heck is going on? The cosine of 90 degrees should be 0, so why am I getting such a deviance... and more importantly how can I stop it?

Answer

Darin Dimitrov picture Darin Dimitrov · May 21, 2011

Let me answer your question with another one: How far do you think 6.12303176911189E-17 is from 0? What you call deviance is actually due to the way floating point numbers are internally stored. I would recommend you reading the following article. In .NET they are stored using the IEEE 754 standard.

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