2016年4月20日SAT考試數學題
來源：
小編：環球教育 522環球教育SAT考試頻道：今天為大家帶來2016年4月20日SAT考試官方每日一題數學部分附答案和解析，希望可以幫助到考生們。
每日一題：
Mathematics>Standard Multiple Choice
Read the following SAT test question and then click on a button to select your answer.
-(a-1)(b-1)(c-1)
Which of the following is equivalent to the expression above?
A. (1-a)(b-1)(1-c)
B. -(1-c)(1-b)(1-a)
C. (c-1)(1-b)(a-1)
D. -(a-1)(1-b)(c-1)
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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