In: Advanced Math
Show that f(x) = x^4+x^3+3x^2+7x−8 is irreducible over Z.
We note that
is irreducible over
if and
only if it is irreducible over 
And
is irreducible over
if and
only if
is irreducible over 
That is,
is irreducible over 
By Eisenstien's criteion for
and for
we have
(the first terms coefficient),
(the
coefficients of the rest of the terms) and
(coefficient of the constant term)
Therefore,
is not reducible over 
Which by the above consideration means
is irreducible over 