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A differentiable function is smooth (the function is locally well approximated as a linear function at each interior point) and does not contain any break, angle, or cusp. If x 0 is an interior point in the domain of a function f, then f is said to be differentiable at x 0 if the derivative ′ exists.
A function of a real variable is differentiable at a point of its domain, if its domain contains an open interval containing , and the limit = (+) exists. [2] This means that, for every positive real number , there exists a positive real number such that, for every such that | | < and then (+) is defined, and | (+) | <, where the vertical bars denote the absolute value.
If there exists an m × n matrix A such that = + ‖ ‖ in which the vector ε → 0 as Δx → 0, then f is by definition differentiable at the point x. The matrix A is sometimes known as the Jacobian matrix , and the linear transformation that associates to the increment Δ x ∈ R n the vector A Δ x ∈ R m is, in this general setting ...
3.1 Logarithmic derivatives. 4 Derivatives of trigonometric functions. 5 Derivatives of hyperbolic functions. ... If f and g are n-times differentiable, ...
In the neighbourhood of x 0, for a the best possible choice is always f(x 0), and for b the best possible choice is always f'(x 0). For c, d, and higher-degree coefficients, these coefficients are determined by higher derivatives of f. c should always be f''(x 0) / 2 , and d should always be f'''(x 0) / 3! .
The C 0 function f (x) = x for x ≥ 0 and 0 otherwise. The function g (x) = x 2 sin(1/ x) for x > 0. The function : with () = for and () = is differentiable. However, this function is not continuously differentiable.
If f is a function, then its derivative evaluated at x is written ′ (). It first appeared in print in 1749. [3] Higher derivatives are indicated using additional prime marks, as in ″ for the second derivative and ‴ for the third derivative. The use of repeated prime marks eventually becomes unwieldy.
If f is differentiable at every point in some domain, ... That is, the partial derivative of z with respect to x at (1, 1) is 3, as shown in the graph.