# Getting the Ball Rolling: Domain, Range, Functions, and Relations

🧑Zayn Alazawi 📅June 18, 2020 📊Grade 11 Math

Introduction:

In the realm of mathematics, functions and relations serve as fundamental concepts that form the backbone of various mathematical disciplines. Understanding these concepts is crucial for tackling complex problems in algebra, calculus, and other branches of mathematics. In this article, we will delve into the definitions and properties of functions, relations, domain, and range.

Functions:

A function is a mathematical object that assigns to every element in a set $$X$$ exactly one element in a set $$Y$$. In simpler terms, a function relates each input to exactly one output. The input values, often denoted by $$x$$, belong to the domain of the function, and the corresponding output values, denoted by $$f(x)$$, belong to the codomain. A function is typically represented as $$f:X\rightarrow Y$$:, where $$f$$ is the function, $$X$$ is the domain, and $$Y$$ is the codomain.

Functions are represented using function notation. It's a shorthand method that makes it more convenient to represent and work with functions. The most common form of function notation is $$f(x)$$, where:

1. $$f$$: This is the name of the function. It can be any letter or symbol and is often chosen to represent the nature of the function (e.g., $$g(x)$$, $$h(x)$$, etc.).

2. $$x$$: This represents the input variable. It's the value you plug into the function to get the corresponding output.

3. $$f(x)$$: This is the output of the function given the input $$x$$. It's the result of applying the function to the specific value of $$x$$.

For example, if you have a function $$f$$ defined as $$f(x) = 2x+3$$, you could use function notation to express that if $$x$$ is 4, then $$f(4)$$ would be $$2(4)+3=11$$. So, $$f(4)=11$$.

Function notation is particularly useful when dealing with more complex functions or when expressing relationships in mathematical formulas. It helps in understanding and communicating how a function transforms its input into output, and it's a standard convention used in various branches of mathematics.

Relations:

A relation, on the other hand, is a set of ordered pairs $$(x,y)$$, where $$x$$ is in the domain and $$y$$ is in the codomain. In contrast to functions, a single input value in the domain can be associated with more than one output value in the codomain in a relation. Relations can be represented graphically as points on a coordinate plane, showcasing the pairing of input and output values.

Domain:

The domain of a function or relation is the set of all possible input values for which the function or relation is defined. It is essentially the x-values that make the function or relation meaningful. The domain is a critical aspect as it determines the scope of the function or relation. For instance, a square root function is defined only for non-negative real numbers, and thus its domain is restricted to non-negative values.

Range:

The range of a function or relation is the set of all possible output values that the function or relation can produce. It represents the y-values that the function or relation can attain based on its inputs. Determining the range is crucial for understanding the behavior of a function or relation and its output variability. In some cases, the range may be a subset of the codomain, while in others, it may coincide with the entire codomain.

Conclusion:

In conclusion, functions and relations play pivotal roles in mathematics, offering a structured way to model and understand the relationships between sets of values. The concepts of domain and range further refine our understanding by specifying the input and output values, respectively. A strong grasp of these foundational concepts is essential for students and professionals alike, as they serve as the building blocks for more advanced mathematical studies and applications in diverse fields.

## ✍️Practice

1. Consider the function $$f(x)=3x−2$$.

a) Find $$f(4)$$.

b) Determine the input value ($$x$$) when $$f(x)=7$$.

2. a) $$f(4)=3×4−2=10$$

b) $$3x−2=7$$, solve for $$x$$$$9 = 3x$$ so $$x=3$$

3. Let $$R$$ be the relation defined by $$R=\{(1,2),(3,4),(5,6),(1,4)\}$$

a) Is $$R$$ a function? Why or why not?

b) Find the range of $$R$$.

4. a) No, $$R$$ is not a function because it has the same input (1) paired with different outputs (2 and 4).

b) Range of $$R$$ is $$\{2,4,6\}$$.

5. Given the function $$g(x)=x^2−1$$

a) Determine the domain of $$g(x)$$.

b) Find the range of $$g(x)$$.

6. a) Domain of $$g(x)=x^2−1$$ is all real numbers, $$X\epsilon\mathbb{R}$$.

b) Range of $$g(x)$$ is all real numbers greater than or equal to -1, $$Y\epsilon\mathbb{R}|Y\geq-1$$.

7. Consider the function $$h(x)=\sqrt{x+1}$$​.

a) Determine the domain of $$h(x)$$.

b) Find the range of $$h(x)$$.

8. a) Domain of $$h(x)=\sqrt{x+1​}$$ is $$x≥−1$$ because the expression inside the square root cannot be negative.

b) Range of $$h(x)$$ is $$y≥0$$ because the square root of any real number is non-negative.