prep 2 162

boystar

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?

youngerlee

(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

xianmengyao

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

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