数学prep两道题求教，谢谢

emma-maple

19.        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 variations in sign for the sequence 1, -3, 2, 5, -4, -6 ?

(A) One
(B) Two
(C) Three
(D) Four
(E) Five

 

 

7.         For every positive even integer n, the function h(n) is defined to be the product of all the even integers from 2 to n, inclusive.  If p is the smallest prime factor of h(100) +1, then p is  

(A) between 2 and 10  

(B) between 10 and 20 

(C) between 20 and 30

(D) between 30 and 40  

(E) greater than 40

katherine8110

第一题选c，第二题选e么？

1.问相邻两数乘积为负的数有几对？显然有3对，1×-3，—3×2，5×-4

2，原式=2^50×（1×2×3×……×50）+1

所以h（100）+1除以任何小于50的数都余1

所以p>50

大概是这样吧～

emma-maple

thanks !@@