单选题For all real values of x and y, let x◆y be defined by the equation x◆y = 2 -xy. If -1 a 0 and 0 b 1, then which of the following must be true?A-2a+b-1B-la+b0C0a+blDla+b2E2a+b3
单选题
For all real values of x and y, let x◆y be defined by the equation x◆y = 2 -xy. If -1 < a < 0 and 0 < b < 1, then which of the following must be true?
A
-2<a+b<-1
B
-l<a+b<0
C
0<a+b<l
D
l<a+b<2
E
2<a+b<3
参考解析
解析:
根据题干,发现a= -1/2, b =1/2满足已知条件,a◆b=2-ab,将a= -1/2, b =1/2代入进去,则(-1/2) ◆(1/2) = 2 - (-1/2)(1/2) = 2 + 1/4 = 2.25,故选E。
根据题干,发现a= -1/2, b =1/2满足已知条件,a◆b=2-ab,将a= -1/2, b =1/2代入进去,则(-1/2) ◆(1/2) = 2 - (-1/2)(1/2) = 2 + 1/4 = 2.25,故选E。
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