If 
, then you have
By the intermediate value theorem, there will be some number
such that 
(i.e. 
will have a root in 
) if you can guarantee that 
or 
.
Since the coefficients
are all positive, then you know right away that 
, so you need to have 
in order for there to be such a 
.
This means you need to have
which means (A) must be the answer.
By the intermediate value theorem, there will be some number
Since the coefficients
This means you need to have
which means (A) must be the answer.
