2. A.

3、C

4、D

5、B

6、D

7、D

16，50+50x%

17，x=3a

18,64

19,3

20, 10000

2 1、 1)x = 1 2)y =-3 3)y = 7/4 4)x =-9

22, 1) Substitute Y=4 into the original formula: 1/2*4+M=4M-M to get M= 1.

2) Substitute X= 1/2 into 1 to get M=5, and substitute M=5 into 2 to get:

1/4*(-4*25+2*5-8)-( 1/2*5- 1)= -26