Verified answer

Here's how to tell:

If there is no x in the equation (the equation looks like y = b), then it is horizontal.

If there is no y in the equaion (looks like x = a), then it is vertical.

If there is both an x and a y, then it is diagonal.

In this case, there is both an x and y, so this is diagonal.

Diagonal

diagonal. Just think about the graph of y=x. It is diagonal. Therefore, anything of that form must also be diagonal.