  We present a necessary and sufficient condition for a cubic polynomial to be
positive for all positive reals. We identify the set where the cubic polynomial
is nonnegative but not all positive for all positive reals, and explicitly give
the points where the cubic polynomial attains zero. We then reformulate a
necessary and sufficient condition for a quartic polynomial to be nonnegative
for all positive reals. From this, we derive a necessary and sufficient
condition for a quartic polynomial to be nonnegative and positive for all
reals. Our condition explicitly exhibits the scope and role of some
coefficients, and has strong geometrical meaning. In the interior of the
nonnegativity region for all reals, there is an appendix curve. The
discriminant is zero at the appendix, and positive in the other part of the
interior of the nonnegativity region. By using the Sturm sequences, we present
a necessary and sufficient condition for a quintic polynomial to be positive
and nonnegative for all positive reals. We show that for polynomials of a fixed
even degree higher than or equal to four, if they have no real roots, then
their discriminants take the same sign, which depends upon that degree only,
except on an appendix set of dimension lower by two, where the discriminants
attain zero.
