The expression  has always the same sign as,  if
a)		b)		c)		d)

(b)

Let  Then,

Thus, the curve  meets -axis at

If  then by hypothesis  This means that the curve  does not meet -axis

If  then by hypothesis,  which means that the curve  is always below -axis and so it does not intersect with -axis

Thus, in both the cases  does not intersect with -axis  for any real

Hence,  i.e.  has imaginary roots and so we have