Question

Does this graph show a function? Explain how you know.

Answer 1

Answer: D) No. The graph fails the vertical line test.

Explanation:

We are able to draw a single vertical line that passes through more than one point on the red curve. For example, we could draw a vertical line through x = 5 and have it cross the red curve at (5,4) and (5,-4).

So this is one example where the graph fails the vertical line test. It passes this test when such a thing doesn't happen. In other words, a function is only possible if any x input leads to exactly one and only one y output.

In this case, x = 5 leads to multiple outputs y = 4 and y = -4 at the same time. There are other x values which this occurs as well (any x values such that x > 1). So this is why we don't have a function.