[求助]prep 上的数学

for a finite sequence of nonzore number ,the number of variations in sign is defined as the number of pairs of  consecutive of sequence for which the product of the two consecutive terms is negative  ,what's the number of variations in sign for  the sequence 1 　－３　２　５　－４　－６？

ａｎｓｗｅｒ　：３

顶，题目也不知道是啥意思

我想这道题目是这样的，题目中要我们求the number of variations in sign，并全对variations in sign进行了定义，为连续相乘的两个数的积为负数。那么会出现哪些情况满足以上的定义

I 1*-3=-3

II -3*2=-6

III 5*-4=-20

个人认为如此