3. 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 term is negative. What is the number of variations in sign for the swquence 1, -3, 2, , -4, -6 ?
a. one
b. two
c. three
d. four
e. five
A: c
這一題我看不懂題目所說的是什麼意思,可以幫忙解釋嗎?謝謝