How to check if Math.cos(angle) = 0

Question

I am trying to find the correct domain for the tan function, I know that

tan x = sinx / cos x

and tan is undefined when cos x = 0. So

I am trying to check if cos x is 0.

 if ( Math.Cos(x).Equals(0) )
 {
     // do stuff
 }

But this is never true because Math.Cos returns 6.123....E-17 How o check for cos == 0 ?

Answer 1

You need to broaden your expectations a bit - in order for Math.Cos(x) to be genuinely equal to 0, you'd either need inaccuracy in Cos (which will happen, of course) or for x to have an irrational value.

Instead, you should work out some tolerance - some range of values for Math.Cos which is very close to 0. For example:

if (Math.Abs(Math.Cos(x)) < 1e-15)

That 1e-15 is picked pretty much arbitrarily - you should work out what you want it to be for your particular task. (This will still give pretty enormous tan values, of course...)