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标题: [求助] 几道prep08数学题求助 [打印本页]

作者: 2012冲刺317 时间: 2012-2-19 11:14
标题: [求助] 几道prep08数学题求助
刚刚开始看数学，有几道prep08弱题求助，恳请大牛指点！

DS:
Is M+Z>0?
(1) M-3Z>0
(2) 4Z-M>0

PS:
If X is positive, which of the following could be the correct ordering of 1/X, 2X and X^2?
(i) X^2 < 2X < 1/X
(ii) X^2 < 1/X < 2X
(iii) 2X < X^2 < 1/X

PS:
At a dinner party, 5 people are to be seated around a circular table. Two seating arrangements are consider different only when the positions of the people are different relative to each other. What is the total number of different possible seating arrangements for the group?

作者: amandasisco 时间: 2012-3-30 06:00

刚刚开始看数学，有几道prep08弱题求助，恳请大牛指点！

DS:
Is M+Z>0?
(1) M-3Z>0
(2) 4Z-M>0

PS:
If X is positive, which of the following could be the correct ordering of 1/X, 2X and X^2?
(i) X^2 < 2X < 1/X
(ii) X^2 < 1/X < 2X
(iii) 2X < X^2 < 1/X

PS:
At a dinner party, 5 people are to be seated around a circular table. Two seating arrangements are consider different only when the positions of the people are different relative to each other. What is the total number of different possible seating arrangements for the group?

-- by 会员 2012冲刺317 (2012/2/19 11:14:39)

No 1
I did wrong also. any 1 or 2 alone is not sufficient. do you agree?
If combined, 1+2 can deduce that z>0
and then 3z<m<4z, so m>0
Obviously, 1+2 sufficient

No 2
pay attention to could be
1/X, 2X and X^2
if x>1, could be 1/x<2x< x^2
if 0<x<1, could be x^2 < 2x < 1/x or x^2 < 1/x < 2x
if x<-1, could be 2x<1/x<x^2
if -1<x<0, could be 1/x<2x<x^2

(i) X^2 < 2X < 1/X
(ii) X^2 < 1/X < 2X
(iii) 2X < X^2 < 1/X

So iii is impossible. i and ii is maybe true.

No 3
first, just consider in the ordinary mode, it is clear that should be 5*4*3*2*1 = 120
then, consider the overlapped part under the circumtance.look below:
ABCDE should be same as BCDEA, CDEAB, DEABC and EABCD
So 120/5=24

作者: MANLON 时间: 2012-3-30 09:25
我数学不好，还是没懂，麻烦再说细点，第三题，谢谢哈

作者: ft228592139 时间: 2012-3-30 09:51

-- by 会员 2012冲刺317 (2012/2/19 11:14:39)

第三题“Two seating arrangements are consider different only when the positions of the people are different relative to each other”的意思就是说ABCDE,BCDEA,CDEAB,DEABC和EABCD这种五排列方式是同一种position，因为围在一个圆桌上这样的排列方法看起来是一样的，所以正确答案为5*4*3*2*1/5=24

作者: 憨憨528 时间: 2012-3-31 20:00
第二题把这三个函数在坐标系中表示出来，一比就能看出有哪几种可能了

作者: Espange 时间: 2014-10-24 18:14
第二题说If X is positive。。。不能取负数吧？2L讨论错了~

作者: 大海一直在路上 时间: 2015-6-18 21:05
请问能把数学的题和笔记给我一下么谢谢啦怎么都找不到

作者: gar_bbbbb 时间: 2017-8-7 11:08
作为一个手残，把图画出来了但是偏差太大还是没有算对。画了一个标准的TAT。希望下次要细心。

作者: 梦季 时间: 2018-5-23 10:15
看一下！

作者: 梦季 时间: 2018-5-23 12:01
看一下！

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