Răspuns:
Explicație pas cu pas:
ex11
A={3,4,5,6,7,8,9,10,11,12}, B={3, 6, 9, 12}. ⇒B⊂A, deoarece toate elementele multimii B se contin in multimea A
ex12
X={1,2,3,4,5,6,7,8,9},
2≤3·y-1≤26 |+1, ⇒2+1≤3·y-1+1≤26+1, ⇒3≤3·y≤27 |:3, ⇒1≤y≤9
Deci Y={1,2,3,4,5,6,7,8,9}, ⇒X = Y
ex13
a) M={2,3,4,5},
b) 4 elemente
c) {2,3}, {2,4}, {2,5}, {3,4}, {3,5}, {4,5}.