Answers:
Graph A is a function
Graph B is not a function
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Explanation:
To check if we have function or not, we apply the vertical line test. This test is where you ask yourself: "Is it possible to draw a single vertical line through more than one point on the curve?"
If the answer to that question is "yes it is possible", then we do not have a function. Graph B shows that we can draw a line through say x = 2 and have the vertical line intersect at points (2,2) and (2,4). The input x = 2 leads to multiple outputs y = 2 and y = 4 simultaneously. This is why graph B is not a function.
A function is only possible when any x input from the domain leads to exactly one y output in the range. Graph A is a function because we cannot draw a single vertical line to intersect through that curve more than once.