Vertical Line Test

The vertical line test can be used to determine if a curve is the graph of a function. The vertical line test determines if for every value of x there is only one output y corresponding to it. The picture below shows the graph of the function and the line . By adjusting the values of , check that passes the vertical line test, i.e. for every value of there is only one output corresponding to it.

Graph of h(x)

What about the curve below, does it pass vertical line test? Does this curve represent a function? Explain why.
Can you think of what features a curve must have to be the graph of a function? Perhaps contrast these two graphs.