Functions are the backbone of mathematics, and they play a key role in almost everything we do. Therefore, understanding what a function is, how it works, and how to recognize different functions is essential for anyone who wants to do well in mathematics. One of the main things that students learn about functions is that they can increase or decrease, depending on their properties. In this article, we’ll take a closer look at which functions are increasing, and how you can identify them.
What is a function?
Before we dive into the topic of increasing functions, let’s first make sure we’re all on the same page regarding what a function is. A function is a rule that assigns a unique output to each input. The input is also known as the independent variable, while the output is known as the dependent variable. For example, suppose we have a function f(x) that takes an input of x and outputs x+2. In this case, we can say that f(3) = 5, because when we plug in the input x=3, we get an output of 5.
What does it mean for a function to increase?
When we say that a function is increasing, we mean that as the input increases, the output also increases. In other words, if we have a function f(x) and we increase the value of x, we can expect the value of f(x) to also increase. Geometrically, this would correspond to a graph that is sloping upwards from left to right on a coordinate plane.
How can you tell if a function is increasing?
There are a few different ways to tell if a function is increasing. One of the easiest ways is to look at the graph of the function. If the graph is sloping upwards from left to right, then the function is increasing. Another way to tell is by looking at the derivative of the function. If the derivative is positive for all values of x, then the function is increasing.
Using the graph to identify increasing functions
To illustrate the concept of increasing functions, let’s take a look at some examples. First, consider the function f(x) = x + 2. If we graph this function, it would look like this:
x  2  1  0  1  2 
f(x)  0  1  2  3  4 
As you can see from the graph, the graph is sloping upwards from left to right. Therefore, we can conclude that the function is increasing.
Using the derivative to identify increasing functions
Another way to tell if a function is increasing is by looking at its derivative. The derivative of a function is basically the slope of the function at any given point. If the derivative is positive for all values of x, then the function is increasing. For example, let’s consider the function g(x) = x^2. The derivative of this function is 2x. If we set the derivative equal to 0, we get x=0. This means that the function has a minimum value at x=0, and is increasing for all other values of x.
The most common types of increasing functions
Linear functions
A linear function is a function that has a constant slope. In other words, as the input increases by a certain amount, the output also increases by the same amount. For example, the function f(x) = 2x is a linear function with a slope of 2. As x increases by 1, f(x) increases by 2.
Polynomial functions
A polynomial function is a function that has one or more terms, where each term is a constant multiplied by a power of x. For example, the function f(x) = x^2 + 2x + 1 is a polynomial function with three terms. As x increases, the function will either increase or decrease, depending on the degree of the polynomial.
Exponential functions
An exponential function is a function that has a variable in the exponent. For example, the function f(x) = 2^x is an exponential function. As x increases, the function will increase exponentially.
Trigonometric functions
Trigonometric functions are functions that involve trigonometric ratios, such as sine, cosine, and tangent. These functions can increase or decrease depending on the domain and range of the function.
Why is it important to know which functions are increasing?
Understanding which functions are increasing is important in many areas of mathematics and science. For example, in calculus, the concept of increasing functions is essential for understanding the behavior of functions and finding the maximum and minimum values of a function. In physics, the concept of increasing functions is used to study the rates of change of different phenomena.
Conclusion
Knowing which functions are increasing is essential for anyone who wants to be proficient in mathematics and related fields. By understanding the different types of increasing functions and how to identify them, you can gain a deeper appreciation for the beauty and complexity of mathematics.
FAQs

Q: Can a function be increasing and decreasing at the same time?
A: No, a function can either be increasing or decreasing, but not both. 
Q: What happens if a function is neither increasing nor decreasing?
A: If a function is neither increasing nor decreasing, it is said to be constant. 
Q: What is the difference between a linear and a polynomial function?
A: A linear function has a constant slope, while a polynomial function has one or more terms, where each term is a constant multiplied by a power of x. 
Q: How can I tell if a function is increasing or decreasing on a particular interval?
A: To determine if a function is increasing or decreasing on a particular interval, you need to look at the sign of the derivative on that interval. If the derivative is positive, the function is increasing. If it is negative, the function is decreasing.
References
 Burden, R. L., & Faires, J. D. (2020). Numerical analysis (10th ed.). Cengage Learning.
 Stewart, J. (2015). Single variable calculus: early transcendentals (8th ed.). Cengage Learning.
 Tan, S. T. (2019). Applied calculus for the managerial, life, and social sciences: A brief approach (10th ed.). Cengage Learning.