When I type =cos(45) in cell A1, it returns 0.525322 which is not
1/Sqrt(2). Does anyone have any suggestions on how to use Cos?
As Niek noted, COS() expects radians, not degrees, a fact that is
explained clearly, even by example, on the Help page. Click on Help
=> Microsoft Excel Help => Search For: COS => COS Worksheet. That is
not intended to be an "RTFM" comment, but to introduce you to the Help
feature, which will be useful in the future.
But note that even COS(RADIANS(45)) does not equal 1/SQRT(2). If you
subtract the two, you will see a difference of about 1E-16. That's to
be expected, given the different approximation formulas used
internally.
(For the nitpickers, arguably Excel could have ensured equality in
this particular case by using a table look-up, as it probably does for
"common" arguments of functions like COS, RADIANS and SQRT, and it
controls the result of RADIANS(45). But that would be the exception,
not the rule.)
