#### Answer

Not a function

#### Work Step by Step

In order to determine whether an equation is a function or not, we examine the shape of the function. (If you do not recall the shape, you can graph the function to better visualize it.) We then apply the vertical line test, which states that if a vertical line can pass through the function twice at any input value, it is not a function, and if a vertical line cannot pass through the function twice at any input value, it is a function. Considering this, we find that the given equation is not a function, for it is the graph of a vertical line.