The relation {(-3, 6), (-2, 7), (-1, 8), (0, 9)} are a function because they pass the vertical line test. If a vertical line intersects a curve on an *xy*-plane more than once then for one value of x the curve has more than one value of y so the curve does not represent a function. If a vertical line intersects a curve only once then the curve represents a function.

**How to determine whether a relation is a function**

Although the problem is slightly different to the one in the question, I recommend you check out this YouTube clip by *TabletClass Math* about working out whether a relation is a function.

I don't know about you, but I find it easier when these things are visually explained to me: