Let <I>F</I> be a field. If <i>f(x)</i>  belongs to <i>F[x]</i> and <i>deg f(x)</i> is  2 or 3, then <i>f(x)</i> is
reducible over <i>F </i>if and only if <i>f(x)</i> has a zero in <i>F.</i>