Exercise 10, § 2

Let $f$ be a nonzero element of $\mathbf{Z}[X_1, ..., X_n]$. Let $N(q)$ be the number of zeros of $f$ in the box $|x_1| \leq q, ..., |x_n| \leq q$. Then $N(q)/q^n$ tends to 0 when $q \to + \infty$.