Remember: The derivative of a function

*f*at*x*=*a*, if it even exists at*x*=*a*, can be geometrically interpreted as the slope of the tangent line drawn to the graph of*f*at the point (*a, f(a))*. Hence, the y-coordinate (output) of the pink point = the slope of the tangent line drawn to the graph of*f*at the**BIG BLACK POINT**. (Note that the**pink point**and the**BLACK POINT**always have the same x-coordinate.)