How to do logs with non-standard bases on my TI calc

[J3anyus]

I'm doing some logarithm stuff for math, and I need to do logarithms with non-standard bases (base 5, base 7, etc.). TI calculators can only do logs in base 10, but I remember there's some way to convert a non base 10 logarithm to base 10 pretty easily. So, I figured if anyone would know it, ATOT would

So, lets say I want to find out this:

Log base 5 of 0.2

How would I do that using base 10 on my calc? Thanks a ton.

J3

 

[Keego]

Didn't you learn this in math? it's something like
log .2
-------
log 5


(divided)

 

[Keego]

someone with knowledge please step in, I doubt I'm right

 

[Siva]

You are, its called the change of base formula

log base y of x is

log x/log y

not too hard, just divide the log of the number by the log of the base

 

[MajesticMoose]

that's right, but you should have learned that if you're asking how to do it. I just wrote a quick program to do it instead though. Makes things a lot easier.

m00se

 

[J3anyus]

That looks right Siva, thanks.

BTW, I like the Pumpkins quote in your sig. I've always liked that song

 

[LivinLaVivaPollo]

The easiest way for me is to use natural logs. logb5(.02) would be ln(.02)/ln(5)