7. Functions
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For a relation to be a function, each x-value can only be paired with one y-value, but one y-value can be paired with multiple x-values. In a graph, we can check if each x-value has only one y-value by subjecting it to the Vertical Line Test.
On the given graph, there is no visible part where two points have the same y-value. Each vertical line passes through the graph at only one point, so the graph is a function.