Determine Functionality: Is This Graph a Function via the Vertical Line Test?

Vertical Line Test with Complex Curves

Is the given graph a function?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Is the given graph a function?
00:05 The definition of a function is that for each X value there is one Y value
00:09 It appears that for the same X value there are 2 Y values, therefore it's not a function
00:14 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Is the given graph a function?

–7–7–7–6–6–6–5–5–5–4–4–4–3–3–3–2–2–2–1–1–1111222333444555666777–4–4–4–3–3–3–2–2–2–1–1–1111222333000

2

Step-by-step solution

To determine if the given graph represents a function, we use the vertical line test: if any vertical line intersects the graph at more than one point, the graph is not a function.

Let's apply this test to the graph:

  • Examine different sections of the graph by drawing imaginary vertical lines.
  • Look for intersections where more than one point exists on the vertical line.

Upon examining the graph, we observe that there are several vertical lines that intersect the graph at multiple points, particularly in areas with loops or overlapping curves. This indicates that at those x x -values, there are multiple y y -values corresponding to them.

Since there exist such vertical lines, according to the vertical line test, the graph does not represent a function.

Thus, the solution to this problem is that the given graph is not a function.

3

Final Answer

No

Key Points to Remember

Essential concepts to master this topic
  • Definition: A function has exactly one y-value for each x-value
  • Technique: Draw vertical lines across graph - any line hitting multiple points fails
  • Check: Scan left to right for loops or overlapping sections ✓

Common Mistakes

Avoid these frequent errors
  • Only checking obvious intersections
    Don't just look at clear crossing points = missing subtle overlaps! Complex curves often have hidden loops or self-intersections that aren't immediately obvious. Always systematically scan the entire graph from left to right with imaginary vertical lines.

Practice Quiz

Test your knowledge with interactive questions

Determine whether the following table represents a constant function:

XY02468-3-3-3-3-3

FAQ

Everything you need to know about this question

What exactly am I looking for when I draw vertical lines?

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You're looking for any vertical line that crosses the graph more than once. If you find even one such line, the graph fails the test and is not a function.

How many vertical lines do I need to check?

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You don't need to check every possible line! Focus on areas where the graph curves back on itself, has loops, or appears to overlap. These are the most likely trouble spots.

What if the graph looks really complicated like this one?

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Break it down into sections! Look for obvious loops, spirals, or places where the curve doubles back. Complex graphs often fail the vertical line test in multiple places.

Can a graph be a function if it has curves and bends?

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Absolutely! Curves are fine as long as they don't loop back or overlap vertically. Think of y=x2 y = x^2 - it's curved but still passes the vertical line test.

What does it mean that this graph is 'not a function'?

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It means there are x-values with multiple y-values. In real life, this might represent a relationship where one input can produce different outputs - like a circle where one x-coordinate corresponds to two different heights.

Is there a quick way to spot if a graph will fail?

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Look for closed loops, figure-8 shapes, or any part that curves back over itself. These patterns almost always create multiple y-values for the same x-value.

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