[計量] PP-PS1

[minimumi (米尼)]

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


想請問這題該怎麼解~
謝謝



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推 ddqiii:是三嗎@@?英文好難懂
→ minimumi:答案是C沒錯~怎麼解的啊?
推 metamorphic:題目的意思是問數列裡的變號(variation in sign)次數
→ metamorphic:題目說變號的定義是數列中兩個連續數字乘積為負
→ metamorphic:問該數列有幾個變號 這題可以直接可以看出有三個
→ minimumi:所以正變負,負變正,正變負降子是3個對嗎