Math 2.0

definition

Derivative

Definition

Let II be an open interval, let f ⁣:I→Rf \colon I \to \mathbb{R} be a function, and let a∈Ia \in I. A real number LL is the derivative of ff at aa if lim⁡h→0f(a+h)−f(a)h=L.\lim_{h \to 0} \frac{f(a + h) - f(a)}{h} = L. The notation is f′(a)=Lf'(a) = L.

Remarks

The quotient is the slope of the line through (a,f(a))(a, f(a)) and (a+h,f(a+h))(a + h, f(a + h)). The limit is a limit of a function of hh at 00. The derivative is unique when it exists. For example, the derivative of x2x^2 at aa is lim⁡h→0(2a+h)=2a\lim_{h \to 0} (2a + h) = 2a. Mathlib defines the relation "ff has derivative LL at aa" as HasDerivAt.

Explanations

L1 human

The derivative of ff at aa is the instantaneous rate of change of ff at aa. Geometrically, it gives the steepness of the graph at the point (a,f(a))(a, f(a)).

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  1. Limit point of a set definition
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  3. Derivative definition

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Sources

  1. Web https://en.wikipedia.org/wiki/Derivative, As a limit