13. f (a) represents the derivative of a function f at a point x=a that is the rate of change (of f) at x=a, and also the slope of tangent of the function at x=a. . . . x + a x . . 14. If the 11m1t, 1mgM ex1sts and nite then f must be a ) (1 continuous function of x. 15. For any differentiable function, f, f'(x), is always differentiable on the