作者surfingdream (GMATing)
看板GMAT
标题[计量] 一题pp
时间Sat Jan 17 20:22:29 2009
If the operation @ is defined for all integers a and b by a@b=a+b-ab,which of
the following statements must be true for all integers a,b and c
III)(a@b)@c =a@(b@c)
请问一下上面这个怎麽算出来是true
感谢
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