求教GWD数学3-16

zhouyeying

Q16:
If n is a positive integer and r is the remainder when (n-1)(n+1) is divided by 24, what is the value of r?
(1)      2 is not a factor of n.
(2)      3 is not a factor of n.
   
A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.

如题，请教怎么做啊？

suners

回复 1# zhouyeying


    试试把n按照1、2带入几个数字看看r的值的规律。

season5924

这个是不是选E呀？？

这样做的:

第一个条件说n不能被2整除，假设n=3或n=5，得到的余数不一样，所以不能确定r;

第二个条件说n不能被3整除，假设n=2或n=4，得到的余数不一样，所以也不能确定r。

season5924

看看两个一起的情况哈
不好意思呀，选C，一起的时候就可以了，余数都是0

zhouyeying

thax~~~~