Answer: Top left corner
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Explanation:
Here the graph has each x value correspond to exactly 1 and only 1 y value. Plugging in something like x = 0 leads to y = 3. We do not have multiple outputs for any given input.
The graph passes the vertical line test. This is a test where you see if you can pass a single straight vertical line through more than one point on the red line. In this case, we can't do such a thing, so the graph passes the test.
In contrast, the lower right corner fails the vertical line test because we can draw a single straight vertical line through x = 1 and have it pass through more than one point on the red curve. The same can be said about the lower right corner.
Any graph that is itself a vertical line automatically fails the vertical line test. We have a single input lead to infinitely many outputs. The whole goal of a function is to have one input lead to one output.
Example: say you wanted to convert 100 degrees Celsius to Fahrenheit. Using the proper conversion function, you would input C = 100 and the output would be F = 212. We get exactly 1 and only 1 output. If we got multiple outputs, then we'd have ambiguity of what the proper temperature conversion is.
