en a |(26+c).
3. Prove: if a = b (mod n) and k | n, then a = b (mod k).
4. Determine, with justification, whether Q[x]/(x2 – 9) is an integral domain.
5. Factor x4 + x2 + 1 as a product of monic irreducible polynomials in Z3 .
6. Determine, with justification, whether 10 is a unit in Z18.