Question

A= {x apartine N/ 3x+1 apartine D12} si B={x apartine N/ 14 divizibil (x+3)}

Answer 1

D12= {1;2;3;4;6;12}
3x+1=1 x=0∈N
3x+1=2 x=1/3∉N
3x+1=3 x∉N
3x+1=4 x=1∈N
 3x+1=6 x=5/3∉N
3x+1=12 x=11/3∉N
deci A= {0;1}

D14= {1;2;7;14}
x+3=1 x=-2∉N
x+3=2 x=-1∉N
x+3=7 x=4∈N
x+3=14  x=11∈N
deci B= {4;11}