Răspuns:
Explicație pas cu pas:
A={ n € N | 1/7 < 1/n < 1/2}
1/7 < 1/n
n < 7
1/n < 1/2
n > 2
2 < n < 7
A = {3; 4; 5; 6}
____________
B={n € N | 3/2 > 5/n > 2/3}
3/2 > 5/n
3n > 15
n > 5
5/n > 2/3
2n < 15
n < 15/2
5 < n < 15/2
B = {6; 7}
______________
A U B = {3; 4; 5; 6; 7}
A ∩ B = {6}
A \ B = {3; 4; 5}
B \ A = {7}