[求助]求解一道数学题

emma-maple

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

大家帮个忙，求解思路。

oldmonkeyxu

定义运用题：the number of variations in sign 被定义为在一数列中，相邻两数乘积为负数的个数，本题C

emma-maple

谢谢，麻烦能不能解得详细点，这道题不太会做.

oldmonkeyxu

1, -3, 2, 5, -4, -6 ：（1, -3）  （-3, 2）  （5, -4），这因该明白了吧，阅读要加强呀！

emma-maple

谢谢！