So if I have some, I'll do it over here, log base a of b, and I want to change it to a different base. Let's say I want to change it to base c. This is the same thing as log base c of b divided by log base, log base c of a. Log base c of b divided by log base c of a. And this is a really useful thing. If you've never seen it before, you now have just seen it, this change of base, and we prove it in other videos on Khan Academy. But it's really useful because, for example, your calculator has a log button, but the log on your calculator is log base 10. So if you do log, if you press 10 into your, or 100 into your calculator and press log, you will get a two there. So whenever you just see log of 100, it's implicitly base 10.