Help with simple goniometrics

Hi heres my problem -

tan(α/2) = (*l*/2)/*d*, hence

α = 2*atan(

*l*/2

*d*)

with this formula I can calculate the horizontal field-of-view of my camera.

I found it at this site -

Determining the viewing angle of your camera
Only I havent a scientific calculator or the where with all to solve this!

I need to find a - the angle of view.

I know that l is the width - 2290mm

and I know that d is the distance - 5000mm

Any help from your forum members would be great! please save me any more days trawling endless websites trying to make sense of this!

Thanks

JayT