Choosen As Best Answer

9.
a70 - a57 < 0 --> 越往後面數字越小 --> d < 0
為了方便計算假設該數列
a1, a2, ..., a99, a100
=> 100, 99, ..., 2, 1

(A)
a18 + a51 = 83 + 50 = 133
a20 + a48 = 81 + 53 = 134
--> a18 + a51 < a20 + a48

(B)
d < 0

(C)
S100 不一定小於 0

(D)
a12 + a31 = 89 + 70 = 159
a9 + a34 = 92 + 67 = 159
--> a12 + a31 = a9 + a34
Ans: (A) #

12.
a1 + 6 + a2 + 6 + ... + an + 6
= Sn + (6 * n項)
Ans: (D) #

Post A Comment

解答

News
【IG直播懶人包】十大科目筆記方法分享
【開學必讀】準高中、準大學生必知二三事
【筆記方法】國文筆記怎麼做,三個超強筆記方法大公開