Найдем пересечение множеств А и В:
A = {x | x ∈ Z, x ≥ 9} = {9, 10, 11, 12, 13, ...}
B = {x | x ∈ Z, x < 13} = {..., 11, 12}
A ∩ B = {x | x ∈ Z, 9 ≤ x < 13} = {9, 10, 11, 12}
Ответ: A ∩ B = {9, 10, 11, 12}