Exercise 10, § 2

Let $f$ be a non-zero element of $Z[X_1, ..., X_n]$. Let $N(q)$ be the number of zeros off in the cell $|x_1| \leq q, ..., |x_n| \leq q$. Then $N(q)/q^n$ tends to 0 as $q \to + \infty$.