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. And then we could use that as our approximation for f of 1.9. Well, to do that, we need to know the equation of the tangent line. And we could do that in point-slope form.