In $Z[x]$, let $I=\{f(x) \in Z[x] \mid f(0)$ is an even integer $\}$. Prove that $I=\langle x, 2\rangle .$ Is $I$ a prime ideal of $Z[x] ?$ Is $I$ a maximal ideal? How many elements does $Z[x] / I$ have? (This exercise is referred to in this chapter.)