Answer:
y = (x + 1)(x - 0.586) ( x - 3.414)
Explanation:
I sure wouldn't recommend doing this by trial and error.
I made a graph of which you can see. Every time this monster touches the x axis and speeds away upward is two equal roots of y. So the square root would be one of each of them.
y = (x + 1)^2 (x - 0.586)^2 (x - 3.414)^2
are the listed roots.
The square root is
y = (x + 1)(x - 0.586) ( x - 3.414)
Do I know that this is right? I don't. But I can tell you this: if you multiply 1^2 * (-0.586)^2 * (- 3.414)^2
you get 4 just as you should. Amazing that we have tools that do that sort of thing.