I don't know what they mean by "a single plot."
Since the roots are complex, how are we to graph them?
Draw a single plot showing the parabola
and where the roots are in relation to it.
The roots are: .
Where are they? . . . Well, they are not on the -plane
If we had an -axis coming out of the -plane,
. . the graph might look like this:
| * *
+ - - * - - - - x
One root is on the "floor" at (2,0,1).
The other is (2,0,-1), one unit "behind" the -plane.