x² -5x + 6 > 0 且 x² -5x - 6 ≤ 0 (x-2)(x-3) > 0 且 (x+1)(x-6) ≤ 0x < 2 或 x > 3 且 -1 ≤ x ≤ 6所以 -1 ≤ x < 2 或 3 < x ≤ 6所以非负整数解集是{0 , 1 , 4 , 5 , 6}...