求助几道机经    thank you&nb

janep78

求助几道机经
1. f(n)为小于n并与n没有相同质因子的正整数的个数,当p为任意质数时.f(p)=?

2. 1-n中所有偶数的和为79*80,问奇数n=?

3. a,b两个数刘,a的元素b里都有,问b的标准方差是不是大于a?

4. 直线过点(8,7),求与x轴的截距?
  1).斜率给出
  2).过另一点

[此贴子已经被VICTOR_JZG于2003-1-5 16:07:56编辑过]

[此贴子已经被VICTOR_JZG于2003-1-5 16:09:35编辑过]

VICTOR_JZG

1.
f(p)=p-1,
注意:1不是质数;

lisaislisa

2. 79
1*n+n(n-1)/2*2=79*80=>n(n+1)=79*80=>n=79

3.DS ?
the ans so far is uncertain...

4.D

^^

卧室春竹

第二个 应该是 159

因为是偶数和  所以项数不会是 N

..........

[此贴子已经被作者于2003-1-5 18:57:39编辑过]

VICTOR_JZG

2.
应该是159.

kitten369

For 1) I think it should be f(p)=p-2,(p and 1 are not )

tongxun

kitten369：题目问的是正整数的个数。所以应该是P-1
F（3）后有1、2
F（5）后有1、2、3、4
F（7）后有1、2、3、4、5、6

janep78

3. a,b两个数刘,a的元素b里都有,问b的标准方差是不是大于a?
1.b数列的数学平均值比a大
2.b再20个元素,a有10个

2. 1-n中所有偶数的和为79*80,问奇数n=?

4. 直线过点(8,7),求与x轴的截距?
1).斜率给出
2).过另一点
能否请大侠们详细讲一下这两道题,偶怎么没看明白.

lisaislisa

3. E
since standard deviation emphasis on the difference among the samples , while has little to do with the total numbers or average

2. my mistake again ...-_-!
S=1*x+x*(x+1)*2/2=79*80=>x=79
that is the sum of the even numbers between 1 and n (d=2 )
the  number of them is 79 , since n is a odd number
it is then 79*2+1=159

4.hm... hard to explain if no illustration can i access ....
but the line is certain with two points or with one point and alfa..

^^

kitten369

tongxun, So you count 1 is also  小于n并与n没有相同质因子的正整数的个数.
I guess we have different understanding