So can we figure that out? If f of x is log of x, what is f prime of x? F prime of x, we don't need to use the limit definition. In fact, the limit definition is quite hard to evaluate this limit, but we know how to take the derivative of logarithmic functions. So f prime of x is going to be equal to one over the natural log of our base, our base here, we already talked about that, that is 10. So one over natural log of 10 times, times x. If this was a natural log, well then this would be one over natural log of e times x, natural log of e is just one, so that's where you get the one over x, but if you have any other base, you put the natural log of that base right over here in the denominator.