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A function is defined as the relation between two sets that maps elements of the first to a unique element of the second set.

• The function is denoted as$f:A→B$which shows that function f maps every element of set A to a unique element of set B.
• Vertical line test: The graph of any relationship is a function if it satisfies the vertical line test, which states that if at any point of the graph, we draw a vertical line, then it must intersect the graph at only one point.

In the given relation $x=15$, observe that the graph of the relation is a vertical line. So, the vertical line$x=15$ will intersect the line at many points.

Since the relation does not satisfy the vertical line test, the relation is not a function.

Thus, the given relation is not a function.