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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 f ′ ( x 0 ) {\displaystyle f'(x_{0})} exists.
The global extrema of a function f on a domain A occur only at boundaries, non-differentiable points, and stationary points. If is a global extremum of f, then one of the following is true: [2]: 1 boundary: is in the boundary of A; non-differentiable: f is not differentiable at
This function is continuous on the closed interval [−r, r] and differentiable in the open interval (−r, r), but not differentiable at the endpoints −r and r. Since f (− r ) = f ( r ) , Rolle's theorem applies, and indeed, there is a point where the derivative of f is zero.
Vertical tangent on the function ƒ(x) at x = c. In mathematics, particularly calculus, a vertical tangent is a tangent line that is vertical. Because a vertical line has infinite slope, a function whose graph has a vertical tangent is not differentiable at the point of tangency.
On these points, the function has a derivative of . [11] In 1971, J. Gerver showed that the function has no finite differential at the values of x that can be expressed in the form of 2 A 2 B + 1 π {\textstyle {\frac {2A}{2B+1}}\pi } , completing the problem of the differentiability of the Riemann function.
In summary, a function that has a derivative is continuous, but there are continuous functions that do not have a derivative. [13] Most functions that occur in practice have derivatives at all points or almost every point. Early in the history of calculus, many mathematicians assumed that a continuous function was differentiable at most points ...
[3] [4] A function is said to be symmetrically differentiable at a point x if its symmetric derivative exists at that point. If a function is differentiable (in the usual sense) at a point, then it is also symmetrically differentiable, but the converse is not true.
Rademacher's theorem is a special case, due to the fact that any Lipschitz function on Ω is an element of the space W 1,∞ (Ω). [9] There is a version of Rademacher's theorem that holds for Lipschitz functions from a Euclidean space into an arbitrary metric space in terms of metric differentials instead of the usual derivative.