请教两个prep的问题~~

mereyang

 

1. For a finite sequence of nonzero numbers, the number of variations in sign is defined as the number of pairs of consecutive terms of the sequence for which the product of the two consecutive terms is negative. What is the number of variation in sign for the sequence 1, -3, 2, 5, -4, -6?

 

1. 1
2. 2
3. 3
4. 4
5. 5

 

3. If n and y are positive integers and 450y=n3, which of the following must be an integer?

1. y/(3*22*5)
2. y/(32*2*5)
3. y/(3*2*52)

就这俩题，第一个死活看不懂，第二个死活不会。555，大牛指教~~

3. If n and y are positive integers and 450y=n3, which of the following must be an integer?

1. y/(3*22*5)
2. y/(32*2*5)
3. y/(3*2*52)

就这俩题，第一个死活看不懂，第二个死活不会。555，大牛指教~~

[此贴子已经被作者于2009/7/25 22:39:26编辑过]

mereyang

奇怪了，我已经把重复的删了可是发表出来还是有的。。。晕，大家忽略它

alan722

第一个是两两相邻的数相乘，结果是负数的对数（1，-3），（-3，2），（5，-4）三对

第二个450y是一个数的三次方，又450=3^2*2*5^2,y至少得是3*2^2*5,只有1相除肯定是整数

mereyang

ou 懂了~ thx~