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标题: prep 2 162 [打印本页]

作者: boystar 时间: 2011-5-24 06:54 标题: prep 2 162

162.

If x is an odd integer, which of the following is also an odd integer?

(A) 2x

(B) 4x + 2

(C) x2 + 3

(D) x2 + x + 3

(E) x2 + 2x + 1

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【答案】D

x是奇數假設我用3
代入 D => 3*2+3+3=18 是偶數才對
帶入E ==> 3*2+3*2+1=7 是奇數
那麼應該是E才對呀
錯在哪呢?

作者: youngerlee 时间: 2011-5-24 19:50

(A) 2x

(B) 4x + 2

(C) x^2 + 3

(D) x^2 + x + 3

(E) x^2 + 2x + 1

try again and you will get the answer

作者: xianmengyao 时间: 2011-5-25 06:25

X^2 is odd
X is odd
3 is odd
Odd + odd + odd = odd

Answer E, 2x is even, odd + even + odd = even

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