BackGuidance on Identifying Functions from Graphs
Study Guide - Smart Notes
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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
Examine the graph carefully. For each graph, imagine drawing vertical lines at various x-values.
Ask yourself: Does any vertical line intersect the graph at more than one point? If so, the graph is not a function.
If every vertical line crosses the graph at most once, then the graph is a function.
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.
Review the images below and use the vertical line test to decide for each graph.

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.