So if we wanted to evaluate this, when x is equal to e, then everywhere we see an x, we just have to replace it with an e. This is essentially expressing our derivative as a function of x. It's kind of a crazy-looking function of x. You have a limit here and all of that, but every place you see an x, like any function definition, you can replace it now with an e. So we can, let me just do that. Whoops, I lost my screen. Here we go. So we could write f prime of e is equal to the limit as h approaches 0 of natural log, I'll do the same color so we can keep track of things, natural log of e plus h, I'll just leave that blank for now, minus the natural log of e, all of that over h. So just like that, this right over here, if we evaluate this limit, if we're able to, and we actually can, if we're able to evaluate this limit, this would give us the slope of the tangent line when x equals e. This is doing the formal definition. Now let's do the alternate definition.