The hyperbolic secant is the reciprocal of the hyperbolic cosine.
Therefore, the value of the hyperbolic secant is given by the equation:
Further information on the hyperbolic functions is provided on the Wikipedia Hyperbolic Functions page.The Excel Sech function calculates the hyperbolic secant (sech) of a supplied angle.
Note: the Sech function was only introduced in Excel 2013 and so is not available in earlier versions of Excel.
The syntax of the function is:
Where the number argument is the angle (in radians) that you want to calculate the hyperbolic secant of. This must be between 2^27 and +2^27.
Converting from Degrees to Radians
If your angle is in degrees, you will need to convert it into radians before supplying it to the Sech function. This can be done using the Excel Radians function:
In the following spreadsheet, the Excel Sech Function is used to calculate the hyperbolic secant of four different angles:
Formulas:
 Results:

Note that, in the examples above:
Further details and examples of the Excel Sech function are provided on the Microsoft Office website.
If you get an error from the Excel Sech function, this is likely to be one of the following:
#NUM!    Occurs if the supplied number is less than 2^27 or is greater than 2^27. 
#VALUE!    Occurs if the supplied number argument is not recognized as a numeric value. 