数学jj242

yangxihua · 发表于 2012-5-25 16:52:14

DS 题问xy是否是even number，条件1，x+y 是 even number 条件2 x^2+xy+y^2是even number

gina2012 · 发表于 2012-5-25 17:06:08

1, not sufficient

x=1, y=3, xy=3 or x=2, y=4, xy=8

2. = (x+Y)^2 - xy again depends on X+y is even or not, not sufficient

but togther are sufficient

pengbochina · 发表于 2012-5-29 11:33:13

这题选B吧 (x+y)^2 -xy = even
奇数-奇数=偶 xy是奇数的时候x和y必须都是奇数奇数之和又为偶数所以(x+y)^2必是偶数矛盾
所以xy必是偶数
B

zqf2011 · 发表于 2012-5-29 11:53:18

the answer should be "B"

数学jj242

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