So here it says f prime of five. So this notation, prime, this is another way of saying, well, what's the derivative? Let's estimate the derivative of our function at five. And when we say f prime of five, this is the slope, slope of tangent line, tangent line at five. Or you could view it as the, you could view it as the rate of change of y with respect to x, which is really how we define slope, with respect to x of our function f. So let's think about that a little bit. We see they put the point, the point five comma f of five right over here. And so if we want to estimate the slope of the tangent line, if we want to estimate the steepness of this curve, we could try to draw a line that is tangent right at that point.