Question

Which of these relations is a function? Which number?

Answer 1

Answer:

#1 is the only relation that is a function.

Step-by-step explanation:

The definition of a function is that every x value (within the interval; for continuous functions) has one y value.  This means that one x value CANNOT have two y values and still be a function.  You can use the vertical line test, do this by imagining a vertical line going up and down the graph.  If that line touches two or more points, then that means there are more than 1 y value for at least one of the x values.  That is a quick way to determine if it's a function.  Only #1 passes this test.