Question

det.x €N,15/x-3€N;si 5x-4/x-3€N

Answer 1

x-3 ∈ D 15
x-3 ∈ {1,3,5,15}   +3
x∈ {4,6,8,18}

5x-4/x-3=(5x-15+11)/x-3= [5(x-3)+11]/x-3=5(x-3)/x-3 + 11/x-3= 5 + 11/x-3
x-3 ∈ D 11
x-3∈ {1,11}          +3
x ∈ { 4, 14}