1: 5 * 7 -(2 + 9)

2: (5 * 7) - (2 + 9)

3: 5 * 7 - 2 - 9

4: (5 * 7) - 2 - 9

5: (5 * 7 - 2) - 9

6: [(5 * 7) - 2] - 9

7: 5 * 7 -(9 + 2)

8: (5 * 7) - (9 + 2)

9: 5 * 7 - 9 - 2

10: (5 * 7) - 9 - 2

11: (5 * 7 - 9) - 2

12: [(5 * 7) - 9] - 2

13: 7 * 5 -(2 + 9)

14: (7 * 5) - (2 + 9)

15: 7 * 5 - 2 - 9

16: (7 * 5) - 2 - 9

17: (7 * 5 - 2) - 9

18: [(7 * 5) - 2] - 9

19: 7 * 5 -(9 + 2)

20: (7 * 5) - (9 + 2)

21: 7 * 5 - 9 - 2

22: (7 * 5) - 9 - 2

23: (7 * 5 - 9) - 2

24: [(7 * 5) - 9] - 2

說白了就一種：5*7-2-9