24点游戏2 7 8 9 怎么算

1: (2 × (7 + 9)) - 8
2: 2 × (7 + 9) - 8
3: (2 × (9 + 7)) - 8
4: 2 × (9 + 7) - 8
5: (7 + 9) × 2 - 8
6: ((7 + 9) × 2) - 8
7: (9 + 7) × 2 - 8
8: ((9 + 7) × 2) - 8
用了脑子呢,采纳吧