Published online by Cambridge University Press: 18 February 2016
Let $Q(x,y,z)$ be an integral quadratic form with determinant coprime to some modulus
$q$ . We show that
$q\,|\,Q$ for some non-zero integer vector
$(x,y,z)$ of length
$O(q^{5/8+{\it\varepsilon}})$ , for any fixed
${\it\varepsilon}>0$ . Without the coprimality condition on the determinant one could not necessarily achieve an exponent below
$2/3$ . The proof uses a bound for short character sums involving binary quadratic forms, which extends a result of Chang.