Difference Between Constant Function and Linear Function for JEE Main 2025

A constant function, also known as constant mapping, is a mathematical function where the output remains the same for all possible inputs within its domain. In simpler terms, it is a function that produces a fixed value regardless of the input value.  

• Mathematical Definition: A constant function is represented by an equation of form f(x) = c, where 'c' represents a constant value. This equation signifies that the output (f(x)) is always equal to the constant value 'c' for any input 'x'.

• Graphical representation: The graph of a constant function is a horizontal line parallel to the x-axis. Since the output remains constant, the line has a constant height that does not change as the input varies. In other words, it is a straight line with a slope of zero.

• Constant value: The constant value 'c' in a constant function determines the same output for all inputs. It is important to note that a constant function can have different constant values, each representing a distinct constant function.

• Domain and range: The domain of a constant function is the set of all possible input values for which the function is defined. Since the output remains constant, the range of a constant function consists of a single value, which is the constant value 'c'.

• Constant rate of change: They have a constant rate of change of zero because the output remains the same for any change in the input.

• No inverse function: They are not invertible, meaning there is no inverse function that can map the constant value back to different inputs.

• Contrast with Linear Functions: While a constant function has a constant output, a linear function exhibits a proportional change in the output with respect to the input.

• Example: Let's consider the function f(x) = 5. This equation represents a constant function with a constant value of 5. Regardless of the input value 'x', the output of the function will always be 5. For instance, f(2) = 5, f(0) = 5, f(-3) = 5, and so on.

What is Linear Function?

A linear function is a mathematical function that represents a straight-line relationship between two variables. It is characterized by a constant rate of change, where the output changes proportionally with the input.

• Mathematical Definition: A linear function can be represented by the equation f(x) = mx + b, where 'm' represents the slope of the line and 'b' represents the y-intercept.

• Graphical Representation: The graph of a linear function is a straight line on a coordinate plane. It intersects the vertical (y-axis) at the y-intercept, represented by the value 'b', and has a constant slope, 'm', which determines the steepness of the line.

• Slope: The slope of a linear function represents the rate of change between the output and the input. It indicates how steep or flat the line is. The slope is calculated as the change in y-coordinates divided by the change in x-coordinates between any two points on the line.

• Y-Intercept: The y-intercept is the point where the line intersects the vertical axis (y-axis). It corresponds to the value of 'f(x)' when 'x' is equal to zero. In the equation form, 'b' represents the y-intercept.

• Domain and Range: The domain of a linear function is typically the set of all real numbers, as there are no restrictions on the input values unless the domain of the given function is defined. The range consists of all possible output values, which can span from negative infinity to positive infinity.

• Constant rate of change: They have a constant rate of change, meaning the difference in the output for any two input values is always the same.

• Nature of curve: Linear functions are also continuous and smooth throughout their domain.

• Applications: Linear functions find wide applications in various fields such as physics, economics, engineering, and statistics. They are used to model relationships between variables that show linear behavior, such as distance versus time, cost versus quantity, and temperature versus pressure.

Understanding linear functions is essential in many areas of mathematics and real-world applications.

Difference Between Constant Function and Linear Function

Summary

From this article, it can be concluded that a constant function is a mathematical function where the output remains the same for all possible inputs within its domain, whereas a linear function is characterized by a constant rate of change, where the output changes proportionally with the input. A constant function is represented by an equation of form f(x) = c, where 'c' represents a constant value, while a linear function can be represented by the equation f(x) = mx + b, where 'm' represents the slope of the line and 'b' represents the y-intercept.