求助NN们，几道prep数学难题。

jessy001 · 发表于 2011-8-25 00:46:02

PS:if k≠0,1 or -1,is 1/k>0?
1,1/(k-1)>0
2,1/(k+1)>0
答案A,为什么不是B？k-1不是小于k吗？分母小，整个就会大于1/k,怎么能推出1/k>0?

the function f is defined for all positive integers n by the following rule :f(n)is the number of positive integers each of which is less than n and has no positive factor in common with n other than 1 ,if p is any prime number then f(p)=
p-1 p-2 (p+1)/2 (p-2)/2 2
答案a，这道题迷得不行啊，题都没怎么看完，怎么解啊？

PS:if it tllk Carios 1/2 hour to cycle from his house to the library yesterday ,was the distance that he cycled greater than 6 miles?(note: 1 mile =5280 feet)
1,the average speed at which Carios cycled from his house to the library yesterday was greater than 16 feet per second
2,the average speed at which Carios cycled from his house to the library yesterday was less than 18 feet per second
答案e，为什么不是b？b中不是可以算出cycle的长度小于540feet吗？果断证明问题不能实现，这不也是有效推理吗？还是我理解错了？

谢谢各位！多谢！

bearbaby11 · 发表于 2011-8-25 01:39:56

1/(k-1)>0 -> k-1>0 -> k>1 -> k>0 -> 1/k>0

第二题是说f（p）是这样一个函数：=小于p的并且与p除了1之外没有公因子的所有整数的数量

1.相当于c cycle多于16*30*60/5280miles=5.45
2.c cycle less than 18*30*60/5280miles=6.13
两个范围都不能确定一定大于6

wyw1018 · 发表于 2011-8-25 03:09:24

第二题：
每个数都小于p，并且与p除了1无别的公因子：则说明每个数都与p互质。
因为p是质数，所以与任何小于p的数都互质，因此f(p)=p-1

清谷天 · 发表于 2011-8-25 10:06:32

题中说卡罗花了30分钟（即1800秒）从家到图书馆。1选项说卡罗的速度大于16f每秒,2选项说卡罗的速度小于18f每秒。
换算如下：
1.卡罗走的路程>1800*16f=(1800*16/5280) miles=60/11miles,不能证明距离大于6miles。
2.卡罗走的路程<1800*18f=(1800*18/5280) miles=6.14miles,不能证明距离大于6miles。
1&2,说明距离在（60/11,6.14）之间，不能说明大于6miles。

求助NN们，几道prep数学难题。

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