Vertical Line Test

The vertical line test can be used to determine if the graph of a curve is a function. The vertical line test determines if for every value of x there is only one value of y corresponding to it. The graph shows 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 value of corresponding to it.

Graph of h(x)

What about the graph below, does it pass vertical line test? Is this graph representing 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.