b) E(n)=(3n+5)/(2n-1); E(n) ∈ Z
2n-1 l 3n+5 l×2 ( 2n-1 divide 3n+5)
2n-1 l 2n-1 l×3
2n-1 l 6n+10
2n-1 l 6n-3
------------------- ( - )
2n-1 l 6n+10-6n-(-3) ⇒ 2n-1 l 13 ⇒ 2n-1 ∈ D₁₃
2n-1 ∈ {-13; -1; 1; 13} l₊₁
2n ∈ {-12; 0; 2; 14} l :₂
n ∈ {-6; 0; 1; 7} ∈ Zˣ ⇒ n ∈ {-6; 1; 7}
A = {-6; 1; 7} ∈ Z
