SAT数学备考经典模拟题训练34

>>SAT数学模拟题：SAT数学备考经典模拟题训练34

>>SAT考试辅导

练习题内容

· Question #7: If a·b + b·c + c·a = 0, what is (a + b)2 + (b + c)2 + (c + a)2?

(a) a2 + b2 + c2

(b) 2·(a2 + b2 + c2)

(c) (a2 + b2 + c2)/2

(d) a2 + a + b2 + b + c2 +c

(e) (a + b + c)/2

解析

o Answer: (a + b)2 + (b + c)2 + (c + a)2 = 2·(a2 + b2 + c2) + 2·(a·b + b·c + c·a)

Since a·b + b·c + c·a = 0, the correct result is 2·(a2 + b2 + c2).

o Answer: We need to compare x2 + 1 with x + 1. This results in a comparison between x2 and x.

For some x, x2 will be greater than x, e.g. for x = 2. For others, e.g. x = 1/2, x2 will be lower so the relationship cannot be determined from the information given.

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