**Question:**

We just started Elementary Algebra a couple weeks ago after frustration with Saxon. We are struggling with Chapter 2, Less 3, #6. How do I teach my son to determine if these graphed coordinates are a function? He understands the tables and graphing formulas…but we are getting tripped up on #6. Please help! 🙂

**Answer from Dr. Callahan:**

The key here is pretty simple.

A function can only have ONE Y value for every X value. To see this on the chart, look for any place where you can draw a straight vertical line and cross TWO or more of the points in the function.

For instance – in a) you cannot. Any vertical line will only cross one point. So x = 1 will get y = 1 (assuming each block is 1)

But, for c) you can see that this is NOT the case. When x=2, you have y = 0, or y=2 or y=4. One x with more that one Y is NOT a function. Same applies to g and h.

Does that help?