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Guidance on Identifying Functions from Graphs

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Q7–Q10. Determine whether the graph is a graph of a function of x.

Background

Topic: Functions and Graphs

These questions test your understanding of what qualifies as a function based on its graph. In calculus, a function is a relation where each input (x-value) corresponds to exactly one output (y-value). The most common graphical test for this is the "vertical line test."

Key Terms and Concepts:

  • Function: A relation in which every x-value has only one y-value.

  • Vertical Line Test: If any vertical line crosses the graph more than once, the graph does not represent a function.

Step-by-Step Guidance

  1. Examine the graph carefully. For each graph, imagine drawing vertical lines at various x-values.

  2. Ask yourself: Does any vertical line intersect the graph at more than one point? If so, the graph is not a function.

  3. If every vertical line crosses the graph at most once, then the graph is a function.

  4. Apply this reasoning to each graph provided. For example, a straight line or a parabola typically passes the vertical line test, while a circle does not.

  5. Review the images below and use the vertical line test to decide for each graph.

Graph of a straight line Graph of a parabola Graph of a curve on the right side Graph of a circle

Try solving on your own before revealing the answer!

Final Answer:

  • Q7 (image_1): Function (passes vertical line test)

  • Q8 (image_2): Function (passes vertical line test)

  • Q9 (image_3): Function (passes vertical line test)

  • Q10 (image_4): Not a function (fails vertical line test)

The vertical line test is a quick way to determine if a graph represents a function. If any vertical line crosses the graph more than once, it is not a function.

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