怎样用2 6 9 9用加减乘除法得24

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