javascript - Math.cos() gives wrong results

According to my understanding, and my calculator, cos(90
degrees) equals 0.
In my code, I have a
function that allows me to type in degrees whenever I need
to:

function
            deg(i)
{
 return
            i*Math.PI/180;
}

Although,
when calling Math.cos(deg(90)); the output I receive is
6.123233995736766e-17.

Why
could such a thing possibly
happen?

(Please excuse me for my bad
English)

Answer

deg(90) is
approximately equal to 90*Math.PI/180 and
your result is aproximately equal to
0.

So, everything is
fine ;)

Note that it has to be
approximate, because there is no way to represent π
precisely.