So the function might look, might look something like this. We're trying to figure out what f of 1.9 is. So if x is 1.9, f of 1.9, if that's the way the function actually looked, might be this value right over here. But we don't know for sure because we don't know much more about the function. But what they're suggesting for us to do is use this tangent line. If we know the equation of this tangent line here, we could say, well, what does that tangent line equal when x equals 1.9? When x equals 1.9, it equals that point right over there.