(4n+7)/(2n-1) = [2(2n-1)+9]/(2n-1) =
= 2 + 9/(2n-1)
2n-1 ∈ D₉ ⇔ 2n-1 ∈ {-9; -3; -1; 1; 3; 9}⏐+1
⇔ 2n ∈ {-8; -2; 0; 2; 4; 10}⏐: 2