Mathematics
Grade 10
15 min
Identify functions vertical line test
Identify functions vertical line test
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1
Introduction & Learning Objectives
Learning Objectives
Define a relation and a function.
Explain the purpose and procedure of the vertical line test.
Apply the vertical line test to a given graph to determine if it represents a function.
Distinguish between graphs of functions and non-functions, including linear equations.
Connect the outcome of the vertical line test to the definition of a function.
Analyze the graphs of individual equations within a system to verify they are functions.
Can a person be in two different places at the exact same time? 🤔 The vertical line test helps us check for impossible situations like this on a graph!
In this tutorial, you will learn a simple visual method called the Vertical Line Test to quickly identify if a graph represents a function. This is a foundational skill for...
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Key Concepts & Vocabulary
TermDefinitionExample
RelationAny set of ordered pairs (x, y). It describes a relationship between two sets of values, the inputs and the outputs.The set {(1, 5), (2, 10), (2, 11), (3, 15)} is a relation.
FunctionA special type of relation where every input (x-value) is paired with exactly one output (y-value). No x-value can be repeated with a different y-value.The set {(1, 5), (2, 10), (3, 15)} is a function. The previous example is not, because the input 2 has two different outputs (10 and 11).
DomainThe set of all possible input values (x-coordinates) for a relation or function.For the function {(1, 5), (2, 10), (3, 15)}, the domain is {1, 2, 3}.
RangeThe set of all possible output values (y-coordinates) for a relation or function.For the function {(1, 5), (2, 10), (3, 15)}, the range...
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Core Formulas
Definition of a Function
For a relation to be a function, for every x in the domain, there must be exactly one y in the range.
This is the fundamental principle that the vertical line test visually checks. If an x-value has more than one y-value, the relation is not a function.
The Vertical Line Test
A graph represents a function if and only if no vertical line can be drawn that intersects the graph at more than one point.
Use this test by imagining or drawing a vertical line and sweeping it across the entire graph from left to right. If the line ever touches the graph in two or more places simultaneously, the graph does not represent a function.
Equation of a Vertical Line
x = c
This is the general equation for a vertical line, where 'c' is the x-value at...
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Challenging
A piecewise graph is defined by y = x for x < 2 and y = -x + 6 for x ≥ 2. When applying the vertical line test at exactly x = 2, how many times does the line intersect the graph?
A.Zero times, because there is a break at x=2.
B.Two times, at y=2 and y=4, so it is not a function.
C.One time, at the point (2, 4), so it passes the test at this point.
D.One time, at the point (2, 2), so it passes the test at this point.
Challenging
The graph of a circle x² + y² = 16 fails the vertical line test. Which of the following modifications to the relation would result in a graph that IS a function?
A.Restricting the domain to 0 ≤ x ≤ 4.
B.Restricting the range to y ≥ 0.
C.Restricting the domain to -4 ≤ x ≤ 4.
D.Restricting the range to -4 ≤ y ≤ 4.
Challenging
A system of equations includes the relation x = 4. Applying the vertical line test to the graph of x=4 shows it is not a function because the input x=4 corresponds to infinite outputs. How does this relate to the algebraic nature of the equation?
A.It shows that the equation x=4 can never have a solution in a system.
B.It demonstrates that the equation provides a single value for x but places no restriction on y, allowing one input to map to many outputs.
C.It proves that any system containing x=4 will have no solution.
D.It shows that y is the independent variable and x is the dependent variable.
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