## Formal definition of derivative

### The formal definition of a derivative is a fundamental concept in calculus that represents the rate at which a function is changing at a specific point

The formal definition of a derivative is a fundamental concept in calculus that represents the rate at which a function is changing at a specific point. It provides a precise mathematical definition for expressing how small changes in the input of a function result in corresponding changes in the output.

Let’s consider a function f(x) and a specific point “a” within the domain of f(x). The derivative of f(x) at a, denoted as f'(a) or df/dx evaluated at x=a, is defined as the limit of the difference quotient as the change in x approaches zero:

f'(a) = lim(x→a) [f(x) – f(a)] / (x – a)

This definition calculates the slope of the tangent line to the graph of the function f(x) at the point (a, f(a)). It measures how the function f(x) varies near the point a.

In simpler terms, the derivative represents the instantaneous rate of change or the slope of the function at a particular point. It tells us how sensitive the function is to small changes in the input variable.

Derivatives have several applications in various fields, such as physics, economics, engineering, and more. They are used to solve problems involving rates of change, optimization, curve sketching, and understanding the behavior of functions.

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