I'm definitely no mathematician, but wouldn't the Excel SEC() function do the
job?
http://support.microsoft.com/?kbid=213887

if this turns out to be totally off base for your needs, be gentle, I said I
wasn't a mathematician.

"PrincipalSealEngineer" wrote:

Does anyone have a function to calculate secants in excel. Ref
http://mathworld.wolfram.com/SecantMethod.html