1.Let p_1,p_2 e Z[x]. Z[p_1,p_2] is subring of Z[x] generated with Z U {p_1,p_2}

are Z[x^2 - x^5, x^2 - 2x^5], Z[x^2+x^6,x^2+2x^6] unique factorization domain?

2.Prove that the ring Z[2 *sqrt(-1)]={a+2b* sqrt(-1), a,b e Z} is not principial ideal domain. Is it Euclidean domain?

Please help me.. i'm not good at this, but i need it..