Now there's other notations. If this curve is described as y is equal to f of x, the slope of the tangent line at that point could be denoted as equaling f prime of x one. So this notation, it takes a little bit of time getting used to, the Lagrange notation. It's saying f prime is representing the derivative. It's telling us the slope of the tangent line for a given point. So if you input an x into this function, into f, you're getting the corresponding y value. If you input an x into f prime, you're getting the slope of the tangent line at that point.