Re: Cosine of 90 degrees

"mikelee101" <mikelee101athotmaildotcom> wrote:
I was just curious why I wasn't getting zero for the result of the
cosine of a 90 degree angle. This formula
=COS(RADIANS(90))

I understand your expectation. Even though binary arithmetic often causes subtle differences in results (e.g. IF(10.1-10=0.1,TRUE) returns FALSE!), many implementations of transcendental and other math functions that are implemented with approximating formulas make special cases for recognizable boundary conditions.

For example, that is probably why COS(PI()) is exactly -1.

Since RADIANS(90) returns exactly the same binary result as PI()/2, and PI()/2 is exactly the binary representation of PI() divided by 2, there is no reason why the COS() implementation cannot make a special case of COS(RADIANS(90)) and return exactly zero.

But that's a judgment call. Obviously, the implementors have to draw a line somewhere.


----- original message -----

"mikelee101" <mikelee101athotmaildotcom> wrote in message news:A9F92208-0B96-4629-87D7-C829FB4A3775@xxxxxxxxxxxxxxxx
Hello All,
I was just curious why I wasn't getting zero for the result of the cosine of
a 90 degree angle. This formula

=COS(RADIANS(90))

returns

6.12574E-17

when I would have expected 0. Am I misusing a function in there somewhere?
Any thoughts would be greatly appreciated.

Excel 07, XPPro SP3.

Thanks.
--
Mike Lee
McKinney,TX USA

.

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