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SAT官方每日一题附答案和解析[数学](2016年4月20日)

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答案:C

解析:

Choice C is correct. Subtraction is not commutative. (p-1) is not the same as (1-p).

However, it is true that (1-p)=-(p-1): p-1=space-(-p+1) space=space-(1-p)

We can conclude that when the order of two factors being subtracted in an expression is changed, it is the same as multiplying the original expression by-1.

Start with the original expression -1*(a-1)(b-1)(c-1) and change the order of the subtraction for one set of parentheses: -1*-1*(a-1)(1-b)(c-1)=(a-1)(1-b)(c-1)

Multiplication is commutative, so we can reorder the parenthesized groups to get (c-1)(1-b)(a-1).


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