Intro to Functions & Their Graphs: Videos & Practice Problems

Relations connect X and Y values, represented as ordered pairs, while functions are specific relations where each input has at most one output. To determine if a relation is a function, use the vertical line test: if a vertical line intersects the graph at more than one point, it is not a function. Additionally, when finding the domain of an equation, identify restrictions such as square roots or denominators that cannot equal zero. Understanding these concepts is crucial for analyzing functions and their properties effectively.

Relations and Functions

Understanding the concepts of relations and functions is crucial in mathematics, particularly when analyzing graphs. A relation is defined as a connection between sets of values, specifically X (input) and Y (output) values, which can be represented graphically as ordered pairs. In contrast, a function is a specific type of relation where each input corresponds to at most one output. This distinction is essential: while all functions are relations, not all relations qualify as functions.

To determine whether a relation is a function, one can analyze the inputs and outputs. For instance, if a particular input has multiple outputs, the relation cannot be classified as a function. This can be illustrated through examples where the X values are listed alongside their corresponding Y values. If any X value is associated with more than one Y value, the relation fails the function criteria.

A more efficient method to assess whether a relation is a function is through the vertical line test. This test states that if a vertical line can be drawn on a graph that intersects the graph at more than one point, the relation is not a function. Conversely, if every vertical line drawn intersects the graph at only one point, the relation is indeed a function.

For example, consider two graphs: the first graph fails the vertical line test, indicating that it is not a function, while the second graph passes the test, confirming it as a function. This method simplifies the process of determining the nature of relations and functions, making it easier to analyze complex graphs.

In summary, recognizing the difference between relations and functions, and applying the vertical line test, are fundamental skills in understanding mathematical relationships and graphing. These concepts lay the groundwork for further studies in algebra and calculus, where functions play a pivotal role in modeling real-world scenarios.

State the inputs and outputs of the following relation. Is it a function? {$\left(-3,5\right),\left(0,2\right),\left(3,5\right)$}

• A.
• B.
• C.
• D.

Answer: (C)

State the inputs and outputs of the following relation. Is it a function? {$\left(2,5\right),\left(0,2\right),\left(2,9\right)$}

• A.
• B.
• C.
• D.

Answer: (B)

Example 1

To determine whether a graph represents a function, the vertical line test is a useful method. This test states that if a vertical line can be drawn anywhere on the graph and it intersects the graph at more than one point, then the graph is not a function. Conversely, if every vertical line drawn intersects the graph at most once, then the graph is a function.

For the first graph (Graph A), applying the vertical line test shows that no matter where a vertical line is drawn, it only intersects the graph at a single point. This confirms that Graph A is indeed a function.

In contrast, for the second graph (Graph B), a vertical line can be drawn that intersects the graph at multiple points. This indicates that Graph B does not satisfy the criteria for a function.

Finally, examining the third graph (Graph C) reveals that, similar to Graph A, any vertical line drawn will only intersect the graph at one point. Therefore, Graph C is also classified as a function.

In summary, the graphs that qualify as functions are Graph A and Graph C.

Verifying if Equations are Functions

Understanding whether an equation represents a function is crucial in mathematics, particularly when analyzing graphs and relationships between variables. A fundamental method for determining if a graph is a function is the vertical line test. If a vertical line intersects the graph at more than one point, the graph does not represent a function. Conversely, if it intersects at only one point, it is a function.

When verifying equations as functions, the first step is to solve for y. Once you have y isolated, you need to check if any given x values yield multiple y values. If they do, the equation does not represent a function; if they do not, it is a function. This approach can be summarized: a "yes" answer indicates it is not a function, while a "no" answer confirms it is a function.

For example, consider the equation y + 4 = 3x. Solving for y gives y = 3x - 4. Testing various x values (0, 1, -1, and 2) results in unique y values: -4, -1, -7, and 2, respectively. Since each x corresponds to a single y, this equation is indeed a function. This equation is in the slope-intercept form y = mx + b, where m is the slope (in this case, 3).

Now, consider the equation x² + y² = 25. Rearranging gives y² = 25 - x², and taking the square root results in y = ±√(25 - x²). Testing x = 0 yields y = ±5, indicating that one x value produces two y values (5 and -5). Therefore, this equation does not represent a function. A helpful rule of thumb is that if y is raised to an even power, the equation is likely not a function.

When an equation is confirmed to be a function, it can be expressed in function notation. For instance, the equation y = 3x - 4 can be rewritten as f(x) = 3x - 4, where f(x) denotes the output corresponding to the input x. However, this notation cannot be applied to equations that do not qualify as functions.

In summary, verifying whether an equation is a function involves solving for y and checking for unique outputs for each input. Recognizing patterns, such as the implications of even powers of y, can aid in this process. Understanding these concepts is essential for further studies in mathematics and its applications.

Is the equation $y=-2x+10$ a function? If so, rewrite it in function notation and evaluate at $f\left(3\right)$.

• A. $f\left(3\right)=4$ , Is A Function
• B. $f\left(3\right)=3$, Is A Function
• C. $f\left(3\right)=1$, Is A Function
• D. Is NOT A Function

Answer: (A)

Is the equation $y^2+2x=10$ a function? If so, rewrite it in function notation and evaluate at $f\left(-1\right)$.

• A. $f\left(-1\right)=\sqrt{12}$, Is A Function
• B. $f\left(-1\right)=12$, Is A Function
• C. $f\left(-1\right)=\frac92$, Is A Function
• D. Is NOT A Function

Answer: (D)

Finding the Domain and Range of a Graph

Understanding the domain and range of a function is essential in analyzing its behavior through its graph. The domain refers to the set of all possible x-values, while the range encompasses all possible y-values. A helpful technique for determining these sets is the "squish strategy." To find the domain, visualize squishing the graph down to the x-axis, which reveals the x-values that the function can take. Conversely, squishing the graph down to the y-axis helps identify the range.

When expressing the domain and range, interval notation is commonly used. This notation employs brackets and parentheses: brackets [ ] indicate that a value is included (closed dot), while parentheses ( ) signify that a value is excluded (open circle). For example, if the domain of a function extends from -4 to 5, it can be expressed as [-4, 0) ∪ (1, 4], where the union symbol (∪) connects multiple intervals. Here, the closed circle at -4 and 0 indicates inclusion, while the open circle at 1 indicates exclusion.

Set builder notation is another way to express domain and range, using inequality symbols. For instance, the domain can be represented as {x | -4 ≤ x < 0 or 1 ≤ x ≤ 4}, which conveys the same information as interval notation but in a different format.

To illustrate, consider a graph where the domain is determined by squishing it down to the x-axis. If the resulting intervals are from -4 to 0 and from 1 to 4, the domain is expressed as [-4, 0) ∪ [1, 4]. For the range, squishing down to the y-axis might reveal intervals from -3 to -1 and from 1 to 3, leading to a range of [-3, -1) ∪ [1, 3]. This methodical approach allows for a clear understanding of the function's behavior based on its graphical representation.

Find the domain and range of the following graph (write your answer using interval notation).

• A. Dom: $\left[-5,5\right]$ , Ran: $\left\lbrack-4,4\right\rbrack$
• B. Dom: $\left[-2,2\right]$ , Ran: $\left[-3,3\right]$
• C. Dom: $\left[-4,4\right]$ , Ran: $\left[-5,5\right]$
• D. Dom: $\left(-5,5\right)$ , Ran: $\left(-4,4\right)$

Answer: (C)

Finding the Domain of an Equation

Understanding the domain of a function is crucial in mathematics, particularly when dealing with equations. The domain refers to the set of all possible x-values that can be input into a function without causing any mathematical errors. When determining the domain of an equation, it is essential to identify any restrictions that may arise from the function's structure.

One common restriction occurs when x is inside a square root. For a square root function, the expression under the square root must be non-negative. This means that the values of x must be greater than or equal to zero. For example, consider the function \( f(x) = \sqrt{x} \). To find its domain, we set the inside of the square root greater than or equal to zero:

\[ x \geq 0 \]

This indicates that the domain of \( f(x) \) is from 0 to positive infinity, expressed in interval notation as \( [0, \infty) \). Values below zero would result in a negative number under the square root, which is not permissible.

Another common scenario that imposes restrictions on the domain is when x appears in the denominator of a fraction. In such cases, the denominator cannot equal zero, as division by zero is undefined. For instance, consider the function \( f(x) = \frac{2}{x - 5} \). To find the domain, we set the denominator not equal to zero:

\[ x - 5 \neq 0 \]

Solving this gives us \( x \neq 5 \). Therefore, the domain includes all real numbers except for 5, which can be expressed in interval notation as \( (-\infty, 5) \cup (5, \infty) \).

In summary, when finding the domain of a function represented by an equation, it is vital to identify any values that would lead to mathematical errors, such as negative values under a square root or zero in a denominator. By recognizing these restrictions, you can accurately determine the domain and express it using interval notation.

Find the domain of $f\left(x\right)=\sqrt{x+4}$ . Express your answer using interval notation.

• A. Dom: $\left[4,\infty\right)$
• B. Dom: $\left[-4,2\right]$
• C. Dom: $\left[2,4\right]$
• D. Dom: $\left[-4,\infty\right)$

Answer: (D)

Find the domain of $f\left(x\right)=\frac{1}{x^2-5x+6}$ . Express your answer using interval notation.

• A. Dom: $\left(-\infty,2\right)\cup\left(2,\infty\right)$
• B. Dom: $\left(-\infty,\infty\right)$
• C. Dom: $\left(-2,2\right)\cup\left(2,3\right)\cup\left(3,\infty\right)$
• D. Dom: $\left(-\infty,2\right)\cup\left(2,3\right)\cup\left(3,\infty\right)$

Answer: (D)

Here’s what students ask on this topic:

What is the vertical line test and how is it used to determine if a graph represents a function?

The vertical line test is a method used to determine if a graph represents a function. To apply this test, draw vertical lines through various points on the graph. If any vertical line intersects the graph at more than one point, the graph does not represent a function. This is because a function can have at most one output (y-value) for each input (x-value). If a vertical line intersects the graph at multiple points, it indicates that a single x-value is associated with multiple y-values, violating the definition of a function.

How do you find the domain and range of a function from its graph?

To find the domain of a function from its graph, identify all the x-values that the graph covers. This can be visualized by 'squishing' the graph onto the x-axis. The range is found by identifying all the y-values that the graph covers, which can be visualized by 'squishing' the graph onto the y-axis. Use interval notation to express the domain and range, where brackets [ ] indicate that the endpoint is included, and parentheses ( ) indicate that the endpoint is not included.

What are the common restrictions when finding the domain of a function from an equation?

When finding the domain of a function from an equation, common restrictions include: 1) The denominator of a fraction cannot be zero, as division by zero is undefined. 2) The expression inside a square root must be non-negative, as the square root of a negative number is not a real number. To find the domain, identify values that make the denominator zero or the inside of the square root negative, and exclude these values from the domain.

How can you verify if an equation represents a function?

To verify if an equation represents a function, solve the equation for y. Then, check if any x-values result in multiple y-values. If each x-value corresponds to only one y-value, the equation represents a function. For example, for the equation y = 3x - 4, substituting different x-values will always yield a single y-value, indicating it is a function. Conversely, for the equation x² + y² = 25, solving for y gives y = ±√(25 - x²), which results in two y-values for some x-values, indicating it is not a function.

What is function notation and how is it used?

Function notation is a way to represent functions using the format f(x), where f denotes the function and x represents the input. Instead of writing y = 3x - 4, you can write f(x) = 3x - 4. This notation clearly shows the relationship between the input (x) and the output (f(x)). It is particularly useful for evaluating functions at specific values, such as finding f(2) by substituting 2 for x in the equation, resulting in f(2) = 3(2) - 4 = 2.