I have a problem with my Excel 2002 that is driving me nuts.

The cosine function returns the wrong answer for the cosine of 90 degrees.
The right answer is zero, of course, but Excel insists on returning a very
small number, 6e-17.

Cosine works fine for all other angles -- both smaller and larger than 90
degrees.

What the heck is going on? Even the simple little calculator that comes
with
Windows gives the right answer.

Can anyone help?

Excel's trig functions don't work in Degrees, they work in Radians. Multiply
your Degrees by PI()/180 to convert them to Radians.

Rick