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