Continuity And Differentiability
Continuity And Differentiability
Continuity and differentiability are two important concepts in calculus. Continuity measures how smooth a function is at a given point, while differentiability measures how fast a function is changing at a given point.
A function is continuous at a point if its limit at that point is equal to the value of the function at that point. In other words, the function does not have a “jump” at that point.
A function is differentiable at a point if its derivative exists at that point. In other words, the function has a welldefined slope at that point.
Continuity is a necessary condition for differentiability, but it is not sufficient. In other words, a function must be continuous at a point in order to be differentiable at that point, but it is not enough.
Differentiability is a stronger condition than continuity. In other words, a function that is differentiable at a point is also continuous at that point, but the converse is not true.
Definition of Continuity
Definition of Continuity
In mathematics, continuity is a fundamental concept that describes the smooth and uninterrupted behavior of a function at a given point. A function is said to be continuous at a point if its limit at that point is equal to the value of the function at that point. In simpler terms, continuity ensures that there are no abrupt jumps or breaks in the graph of a function as we move along the input values.
Formal Definition:
Let (f) be a function defined on an open interval containing the point (c). Then (f) is said to be continuous at (c) if the following condition holds:
$$\lim_{x \to c} f(x) = f(c)$$
This means that as the input value (x) approaches (c), the corresponding output values (f(x)) approach the value (f(c)). In other words, the limit of the function as (x) approaches (c) is equal to the value of the function at (c).
Examples of Continuity:

Linear Function: The function (f(x) = 2x + 1) is continuous at every real number (c). This is because the limit of (f(x)) as (x) approaches (c) is equal to (2c + 1), which is also the value of (f(c)).

Exponential Function: The function (f(x) = e^x) is continuous at every real number (c). This is because the limit of (f(x)) as (x) approaches (c) is equal to (e^c), which is also the value of (f(c)).

Trigonometric Functions: The sine and cosine functions, (sin(x)) and (cos(x)), are continuous at every real number (c). This is because the limits of these functions as (x) approaches (c) are equal to (sin(c)) and (cos(c)), respectively, which are also the values of the functions at (c).
Examples of Discontinuity:

Jump Discontinuity: The function (f(x) = \begin{cases} 1 & \text{if } x < 0 \\ 0 & \text{if } x \ge 0 \end{cases}) is discontinuous at (x = 0). This is because the limit of (f(x)) as (x) approaches (0) from the left is (1), while the limit of (f(x)) as (x) approaches (0) from the right is (0).

Infinite Discontinuity: The function (f(x) = \frac{1}{x}) is discontinuous at (x = 0). This is because the limit of (f(x)) as (x) approaches (0) does not exist. The function approaches infinity as (x) approaches (0).

Removable Discontinuity: The function (f(x) = \frac{x^2  9}{x  3}) is discontinuous at (x = 3). However, this discontinuity is removable by defining (f(3) = 6). This makes the function continuous at (x = 3).
In summary, continuity is a crucial concept in calculus and analysis that ensures the smooth and uninterrupted behavior of functions. It plays a fundamental role in various mathematical operations, such as differentiation and integration, and is essential for understanding the behavior of functions and their graphs.
Definition of Differentiability
Definition of Differentiability
In mathematics, differentiability is a property of functions that measures how smooth the function is at a given point. A function is differentiable at a point if it has a derivative at that point. The derivative of a function is the slope of the tangent line to the function at that point.
Examples of Differentiable Functions
 Linear functions: The derivative of a linear function is a constant.
 Polynomial functions: The derivative of a polynomial function is a polynomial function of one degree less.
 Exponential functions: The derivative of an exponential function is an exponential function with the same base.
 Logarithmic functions: The derivative of a logarithmic function is a logarithmic function with the same base.
 Trigonometric functions: The derivatives of the sine, cosine, and tangent functions are the cosine, negative sine, and secant functions, respectively.
Examples of NonDifferentiable Functions
 The absolute value function: The absolute value function is not differentiable at 0 because the tangent line to the function at 0 is vertical.
 The square root function: The square root function is not differentiable at 0 because the tangent line to the function at 0 is horizontal.
 The function f(x) = x^2 sin(1/x): This function is not differentiable at x = 0 because the limit of the difference quotient does not exist.
Differentiability and Continuity
Differentiability implies continuity, but the converse is not true. A function can be continuous at a point without being differentiable at that point. For example, the absolute value function is continuous at 0, but it is not differentiable at 0.
Applications of Differentiability
Differentiability is used in many areas of mathematics and physics. Some of the applications of differentiability include:
 Finding the slope of a curve: The derivative of a function gives the slope of the tangent line to the function at a given point.
 Finding the rate of change of a function: The derivative of a function gives the rate of change of the function with respect to its independent variable.
 Finding the maximum and minimum values of a function: The derivative of a function can be used to find the maximum and minimum values of the function.
 Solving optimization problems: The derivative of a function can be used to solve optimization problems, such as finding the shortest path between two points or the maximum volume of a container.
Differentiability is a powerful tool that can be used to study a wide variety of problems in mathematics and physics.