2 Definition of the derivative of a function The derivative of f at x is given by f’(x) = lim f(x + ∆x) – f(x) ∆x -> 0 ∆x provided the limit exists. For all x for which this limit exists, f’ is a function of x.
3 Notation for derivatives: f’(x) “f prime of x” dy “the derivative of y with respect to x” dx “ dy – dx” y’ “y prime” d [f(x)] dx Dx[y]
5 Alternative Form of a Derivative f’(c) = lim f(x) - f(c)x c x - c
6 f’(c) = lim f(x) - f(c) x c- x - c f’(c) = lim f(x) - f(c) x c+ x - c The existence of the limit requires that the one-sided limits exist and are equal.f’(c) = lim f(x) - f(c)x c x - c(The derivative from the left)f’(c) = lim f(x) - f(c)x c x - c(The derivative from the right)
7 f is differentiable on the closed interval [a, b] if it is differentiable on (a, b) and if the derivative from the right at a and the derivative from the left at b both exist.
9 Conditions where a function is not differentiable: 1. At a point at which a graph has a sharp turn.2. At a point at which a graph has a vertical tangent line.3. At a point at which the function is not continuous.
10 Theorem: Differentiability Implies Continuity If “f” is differentiable at x = c, then f is continuous at x = c.