This Page is only about how you use them on your calculator.
Recappping, if 53 = 125 then log5 125 = 3
Here we are using 5 as the base of the logarithm, but we can use any number except 0 and 1. Until the coming of the pocket calculator very few people used any base except 10 (for common logarithms) or e (for natural logarithms). On your calculator the log key gives you the common logarithm and the ln key the natural logarithm. To calculate the common logarithm of 1.56 you would enter
To calculate log78 you will enter
The number whose logarithm is x, that is, inverse log x or log-1 x is of course 10x. On the Casio fx series there is a 10x key (and of course ex); on other calculators it may be labelled log-1x. Try ln 7 = and then eAns =
If you want some practice at pushing buttons and have a reasonable understanding of logarithms you might like to prove that