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Graphs of Functions
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Vertical Line Test

Example 4

Graph the following equation:

y= x 2 +4

Then use the vertical line test on each graph to identify if its equation defines y as a function of x.



Solution

Construct a table of ordered pairs. Substitute –1, 0, and 1 for x in the given equation.

Value of
x 		Value of
y= x 2 +4 		Ordered Pair
(x, y)
–1 y=−5 (−1, 5)
0 y=−4 (0, −4)
1 y=−5 (1, 5)

Using the vertical line test, you can see that the graph of y= x 2 +4 is that of a function.