请教Prep一道数学题

sighliny

41.
            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 two sequence for which the product of the two consecutive terms is negative. What is the number of variations is in sign for the sequence. 1, -3, 2, 5, -4, -6
        

Answer:3個
        

实在不明白题目是什么意思，还请各位指点，谢谢啦

sighliny

没人理我啊,自己顶一下。。。。。。。。。。。。。。。。。。。。。