Hi. I took e(-t-T) to mean E^(-t-T)

If you really meant the natural log, then perhaps...

=U*(1-LN(-t-T))

or perhaps w/ cell references: =U*(1-LN(-A1-A2))

Again, I'm not sure I follow, so I'm just throwing this out as an idea.
--
HTH. :)
Dana DeLouis
Windows XP, Office 2003


"Dana DeLouis" wrote in message
...
= U(1-e(-t-T)),

Hi. I don't really follow. I believe the above equation might be written
like this.
Change 't' and 'T' to your cell references.

=U*(1-EXP(-t-T))

Please post back with any further questions. :)
--
HTH.
Dana DeLouis
Windows XP, Office 2003


"Craig" wrote in message
...
Dana Hi, this was of some help but a little hard for me to understand,
here
is the exact equation i wish to put into excel - Um = U(1-e(-t-T)), in my
cells i would have for example A1 = -t, U is constant & T is constant.
could
you help further. i believe the reason the trouble occurs is also because
im
not using LOG im using Natural LOG (NL).

"Dana DeLouis" wrote:

Hi. If I understand the question, the log of say -5 would be a complex
number.
1.609+3.14159 i

If A1 holds -5, then perhaps two ways...

=IF(A1<0,COMPLEX(LOG(ABS(A1)),PI()),LOG(A1))

or more simply the engineering function...
=IMLN(A1)

--
HTH. :)
Dana DeLouis
Windows XP, Office 2003


"Craig" wrote in message
...
im trying to use negative numbers with excel's natural log function,
and
have
found it doesnt work the way im trying it anyway, has anyone out there
used
negative numbers with Excel's natural log function and any sucess?