9 9 6 2四个数字加减乘除每个数字用一次得24，要有过程

1: (9 + 9 - 6) × 2
2: ((9 + 9) - 6) × 2
3: (9 + (9 - 6)) × 2
4: (9 - 6 + 9) × 2
5: ((9 - 6) + 9) × 2
6: (9 - (6 - 9)) × 2
7: 9 × (6 ÷ 9 + 2)
8: 9 × ((6 ÷ 9) + 2)
9: 9 × (2 + 6 ÷ 9)
10: 9 × (2 + (6 ÷ 9))
11: (6 ÷ 9 + 2) × 9
12: ((6 ÷ 9) + 2) × 9
13: 2 × (9 + 9 - 6)
14: 2 × ((9 + 9) - 6)
15: 2 × (9 + (9 - 6))
16: 2 × (9 - 6 + 9)
17: 2 × ((9 - 6) + 9)
18: 2 × (9 - (6 - 9))
19: (2 + 6 ÷ 9) × 9
20: (2 + (6 ÷ 9)) × 9

我晕，你以为是排列啊，写这么多。