## APPLICATION OF DERIVATIVES

Derivatives help us understand how things change. Imagine you’re driving a car and you want to know how fast you’re going at any moment. Derivatives tell you the rate of change of your speed.

Derivatives are used to identify maximum or minimum values of functions. This finds application in economics for profit maximization or cost minimization, and in physics for determining paths of least resistance or optimizing efficiency.

Derivatives are incredibly versatile mathematical tools that have numerous applications across different fields. Here are some key areas where derivatives are extensively used:

- Rate of Change Calculation
- Value Approximation
- Tangent and Normal Line Determination
- Optimization
- Function Behavior Analysis

### RATE OF CHANGE

The concept of rate of change is fundamental in mathematics, particularly within the realm of calculus, and it has numerous practical applications across various fields. Essentially, rate of change describes how one quantity varies concerning another. For instance, within calculus, if we have a function y=f(x), the rate of change of y with respect to x is represented by its derivative \frac{dy}{dx}. This derivative gives us the instantaneous rate of change of y at a specific point, indicating how quickly y is changing concerning x at that precise location.

Rate of change provides insight into how quickly a quantity is changing concerning another. For example, if $y$ represents the position of an object at time $x$, then \frac{dy}{dx} represents the object’s velocity at time $x$.

#### POSITIVE AND NEGATIVE RATES

A positive rate of change indicates an increase in the quantity, while a negative rate of change indicates a decrease. For example, in terms of temperature, a positive rate of change implies a temperature increase, while a negative rate of change suggests a temperature decrease.

#### AVERAGE RATE OF CHANGE

The average rate of change of a function over an interval $[a,b]$ is calculated as \frac{f(b) – f(a)}{b-a} This represents the change in $y$ over the change in $x$ across the interval $[a,b]$.

#### INSTANTANEOUS RATE OF CHANGE

The instantaneous rate of change is the rate at a specific point. It is determined by taking the limit as the interval over which the change is measured approaches zero, which is precisely what the derivative provides.

### MAXIMA, MINIMA AND POINT OF INFLECTION

Maxima and minima are critical points on the graph of a function where it either reaches its highest (maxima) or lowest (minima) value within a particular range. These points are essential in optimization problems where one aims to find the maximum profit, minimum cost, or other extreme values. In real-world scenarios, these points could represent the highest or lowest points of efficiency, production, or any measurable quantity.

Points of inflection indicate locations on the graph where the curvature changes. In simpler terms, if you imagine tracing along the graph of a function, at a point of inflection, you would perceive a shift in the direction of curvature. This change can occur from the graph bending upwards to downwards or vice versa. Understanding points of inflection is crucial for accurately sketching the shape of a function’s graph and comprehending its overall behavior.

### INCREASING AND DECREASING FUNCTIONS

#### INCREASING FUNCTIONS

When we say a function is increasing over an interval, it means that as you move from left to right along that interval, the function’s values consistently go up. In simpler terms, if you pick any two points within that interval, the function’s value at the second point will be greater than the value at the first point. This behavior is visually represented by the graph of the function rising as you move from left to right.

For example, let’s take the function f(x)=x^{2}. As $x$ increases from negative to positive values, the corresponding $f(x)$ values also increase. Hence, for $x≥0$, f(x)=x^{2} is an increasing function.

#### DECREASING FUNCTIONS

Conversely, a function is considered decreasing over an interval if, as you progress from left to right along that interval, the function’s values consistently decrease. In simpler terms, for any two points within that interval, the value of the function at the second point will be lesser than the value at the first point. This trend is depicted by the graph of the function descending as you move from left to right.

For instance, consider the function f(x)=-x^{2}. As $x$ increases from negative to positive values, the corresponding $f(x)$ values decrease. Thus, for $x≥0$, f(x)=-x^{2}is a decreasing function.

### TANGENT AND NORMAL TO A CURVE

#### TANGENT TO A CURVE

A tangent to a curve at a specific point is a straight line that touches the curve precisely at that point, without crossing it. It represents the instantaneous direction of the curve at that point. The slope of the tangent line at any point on the curve is equivalent to the derivative of the curve function at that particular point.

For instance, if we have a curve represented by $y=f(x)$, then the slope of the tangent line at the point x_{0},y_{0} is given by $f’(x_{0})$, where $f’(x)$ is the derivative of $f(x)$ with respect to $x$. The equation of the tangent line can be expressed using the point-slope form as y-y_{0}=f'(x_{0})(x-x_{0})