Answer to: Find and simplify the difference quotient (f(x + h) - f(x))/h for the following function : 8/(2-x). By signing up, you'll get thousands... This is an introductory lesson in Calculus. By taking the limit as h tends to 0 Alan has found the differential of f (a). That is f ' (a) f (a)=a 2 +8. f' (a)=2a. The differential is an equation that gives the value of the gradient of the tangent to the curve for any fixed a value. It is really neat!