I am having a problem with some abstract algebra and I was wondering if anyone could help and give me some insight. The problem is as follows: Give an explanation for your answer, long proof not needed: Determine U(Z[x]) Determine U(R[x]) These are in regards to rings. I know for U(Z[x]) it is something like f(x)=1 g(x)=-1 but I don't know why. As for U(R[x]) I am rather stuck. Any help or nudging in the right direction would be greatly appreciated.