gwd-6-35
The operation O is defined by the equation x O y = (x-y)/(x+y), where y dose not equal to -x. If 3 O y = 5 O 4, then y=
A. 1/9
B.4/15
C.5/12
D.12/5
E.15/4
Answer: D
I lost here completely, have no idea at all. Pls help!
思路:X O y = (x-y)/(x+y)>>>3 O y=(3-y)/(3+y);
>>>5 O 4=(5-4)/(5+4)
又 3 O y = 5 O 4>>>(3-y)/(3+y)=(5-4)/(5+4)>>>Y=12/5
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