Răspuns:
7 | x => x € D7 => x € {1,7}
A = {1,7}
42| (2x-1) => 42| 2x+ 1=> 2x+1€ D42
2x+1€ { 1,2,3,6,7,14,21,42}
2x€ { 0, 1,2,5,6,15,20,41}
x€{0,1:2,1,5:2,3,15:2,10,41:2}
x€ N
din ambele rezulta
x{ 0,1,2,3,10}
B={0,1,2,3,10}
5|(3x+1)=> 3x+1€ D5
3x+ 1 € {1,5}
3x € {0,4}
x €{0,4:3}
x€ N
din ambele rezulta
x=0
C= 0