24点的题目：“5,9,7,2”四个数用加减乘除凑24

1: 5 × 7 -(9 + 2)
2: (5 × 7) - (9 + 2)
3: 5 × 7 - 9 - 2
4: (5 × 7) - 9 - 2
5: (5 × 7 - 9) - 2
6: ((5 × 7) - 9) - 2
7: 5 × 7 -(2 + 9)
8: (5 × 7) - (2 + 9)
9: 5 × 7 - 2 - 9
10: (5 × 7) - 2 - 9
11: (5 × 7 - 2) - 9
12: ((5 × 7) - 2) - 9
13: 7 × 5 -(9 + 2)
14: (7 × 5) - (9 + 2)
15: 7 × 5 - 9 - 2
16: (7 × 5) - 9 - 2
17: (7 × 5 - 9) - 2
18: ((7 × 5) - 9) - 2
19: 7 × 5 -(2 + 9)
20: (7 × 5) - (2 + 9)
21: 7 × 5 - 2 - 9
22: (7 × 5) - 2 - 9
23: (7 × 5 - 2) - 9
24: ((7 × 5) - 2) - 9