How do you use a calculator to calculate a logarithm that isn't base e or ten?

On what kind of calculator? Do you have at least a TI 83?

EDIT: Actually I’m not positive you can do it with an 83, I don’t have mine with me right now, but I am that you can do it with a TI 89. It’s not it’s own button. You have to use the catalogue.

Here’s a tutorial: http://www.prenhall.com/divisions/esm/app/graphing/ti89/homescreen/BasicKeys/other_keys/catalog.html

do you have a scientific calculator? If so, there should be a logx^Y button. Play with that for a while. I think you hit the base # and then hit the log button, put the final number and bang! alternately I’m sure a computer or web-based calculator would do it.

Or you could make it base e or 10.

Google change of base formula,

[for sake of notation LOG 2 (X) is going to be “Log base 2 of X”]

Change of base says that:

LOG z ( Y ) = LOG x ( Y ) / LOG x (Z)

or with real numbers:

LOG 2 ( 3 ) = LOG e ( 3 ) / LOG e ( 2 )

So if your problem is to calculate Log base 7 of (12) you could do ln(12) / ln(7)

@perchik, that’s the one I was looking for. Thanks a bunch!

And, I usually use google as a calculator, for people who had been wondering.

Oh man, good answer Perchik, it just reminds me that I have to know this for my maths exam after Christmas, sigh.