【求助PREP一道奇偶性的题】急！拜谢拜谢！

lovessie

DS题：If x and y are positive integers, is the product xy even?
          (1)5x-4y is even
          (2)6x+7y is even
答案是D EACH statement ALONE is sufficient to answer the question asked

我选了E，想不明白为什么。。。

lauchen

5x-4y=x+4(x-y) 推出x必为even
6x+7y=6(x+y)+y 推出y必为even

lovessie

5x-4y=x+4(x-y) 推出x必为even
6x+7y=6(x+y)+y 推出y必为even

-- by 会员 lauchen (2010/8/12 17:36:29)

天呢。。。我就是弱智。。。我相乘，平方算了半天也没搞明白。。。谢谢！！！！！