And so we want to approximate this y value right over here. We want to approximate that right over here is f of 4.36. And once again, we're assuming we don't have a calculator at hand. So how can we do that using what we know about derivatives? Well, what if we were to figure out an equation for the line that is tangent to the point, to tangent to this point right over here. So the equation of the tangent line at x is equal to four. And then we use that linearization, that linearization to find, to approximate values local to it.