Let A := F q [t] be a polynomial ring over a finite field F q of odd characteristic and let D ∈ A be a square-free polynomial. Denote by N D (n, q) the number of polynomials f in A of degree n which may be represented in the form u•f = A 2 −DB 2 for some A, B ∈ A and u ∈ F × q , and by B D (n, q) the number of polynomials in A of degree n which can be represented by a primitive quadratic form of a given discriminant D ∈ A, not necessary square-free. If the class number of the maximal order of F q (t, √ D) is one, then we give very precise asymptotic formulas for N D (n, q). Moreover, we also give very precise asymptotic formulas for B D (n, q).