[求助]PP3的4道题(2天就考了,拜托了!谢谢!)

salvador

2.IF r and s are intergers and rs+s is odd, which of the following must be even?
a.r
b.s
c, r+s
d. rs-r
e. r^2+s
ANA: C
RS+S 是偶数, 则RS和S必须都是偶数=> S是偶数或R是偶数或都是ODD. => R+S不一定是偶数呀?

lz，题目说RS+S 是奇数，是敲错了还是看错了？

salvador

以下是引用深谷幽兰在2006-4-23 14:35:00的发言：

.IF r and s are intergers and rs+s is odd, which of the following must be even?
a.r
b.s
c, r+s
d. rs-r
e. r^2+s
ANA: C
RS+S 是偶数, 则RS和S必须都是偶数=> S是偶数或R是偶数或都是ODD. => R+S不一定是偶数呀?

lz，题目说RS+S 是奇数，是敲错了还是看错了？

.

明白了. 看的时候把RS+S看成了EVEN.如果是奇数就好做了. 做题真是要仔细呀!

but if rs+s=s(r+1) is odd, s and r+1 should be odd, then r is even and s is odd, r+s is odd.

answer is D? open to discuss

salvador

晕倒了！

这样还是与题目不一致啊！不过这道题我也碰到过，不是很难，到时候仔细一点肯定能作对。

[此贴子已经被作者于2006-4-23 14:52:52编辑过]

salvador

以下是引用scujean在2006-4-23 19:14:00的发言：

.IF r and s are intergers and rs+s is odd, which of the following must be even?
a.r
b.s
c, r+s
d. rs-r
e. r^2+s
ANA: C
RS+S 是偶数, 则RS和S必须都是偶数=> S是偶数或R是偶数或都是ODD. => R+S不一定是偶数呀?

早上想破头就是想不出是C，原来是B

我的做法 rs+s is odd→s(r+1)=积

所以s=积，且(r+1)=积→r=积-1=偶

your answer is a! but the correct answer is b? why?

[此贴子已经被作者于2006-4-23 20:11:59编辑过]