How do I enter an inverse log function into my claculator? for instance log-1(-.4/10)

Hello,
If you want to do correct mathematics you should strive to use the right words to express the concepts, and the right symbols too. While the logarithm function has an inverse function, it is never called an inverse log and it is never represented as log^-1. (I know you are going to protest and claim that the inverse of a sine function is represented on calculators by sin^-1. This a manufacturer shortcut, and we have no power to change that.) HP uses ASIN, ACOS, ATAN. These are still manufacturer shortcuts but they induce fewer errors.
Anyway, the logarithm functions do have inverse functions.

1. Natural loogarithm (ln)

The inverse of the natural log is the exponential.
ln(e^(x))=e^(ln(x)) =x

2. Common logarithm (logarithm in base 10)
The common logarithm has an inverse function, often called the antilogarithm or antilog.

There is an equivalence.
y=log(x) <--> x=10^(y)

From what I undesrtand of your exemple, you are looking for the antilog of the number -0.4/10 (or -0.04.)

-0.04= log(x), what is x?
You use the equivalence above to look for x as follows.
x=10^(-0.04) =0.9120108394.
Use the change sign (-) not the regular MINUS sign.

Take the log of the last result (still stored in Ans memory) and you get the original number.


Hope it helps.