PREP MATHS, HELP!!!

everdeneli

If the interger n is greater than 1, is n equal to 2?
(1) n has exactly two positive facotrs
(2) the difference of any two distinct positive factors of n is odd

Wilt

C吧，1）推出n为质数，2）推出n为偶数

summerice14

agree

everdeneli

If y > = 0, what is the value of x? 1) lx-3l >=y; 2) lx-3l <= y

ANSWER B?

everdeneli

条件2怎么推出偶数呀

spinningtop

刚好做了这题:

factors of 2=1,2.               2-1=odd

factors of 3 = 1,3              3-1=even
factors of 4= 4,1,2             4-1=odd but 4-2=even
factors of 10 = 10, 1, 5, 2.    10-1=odd; 5-1=even

发现只有数字2满足条件, 所以确定条件2是充分的

hjsh0204

同意楼上的，认为答案是B

(2) the difference of any two distinct positive factors of n is odd

在n的factors里面，一定有一个是1。

而the difference is odd,所以另一个factor必定是偶数。

最后，偶数的factor还不能多于一个，不然他们相差又不是odd.

所以n之有1,2两个factor.

Wilt

恩，有道理，2）可以直接推出n=2  应该为B

一开始误导了不好意思丫~