thank you elasti.

 

ok, at x=-4, g(x) =-128. Its gone off the graph. So, if p =0, f(x) = g(x) will have 3 roots. So just tug the graph down by making p<0. That way you remove the solution x=0 and so, we get two real roots.

 

Again, if you increase p just beyond 3, then for all x>0, f(x) becomes +ve, but a new root emerges near x=-4. But you cant increase p beyond 128 as then as I have written in my previous post, there are no real solutions