Question

Sarah

求計算過程

A
有一等差級數共有 45 項,其q + a, =-23 , aa + as = -5,則此等差級數的和為多少?
( ssait d = -25
(A) -315 (B) - 215 (C) -630 (D) - 600
Isait and = -5
觀察下列兩個等差数列:
J-
甲数列:2,5,8,11,14,17,
8643
4
201=
B C#:
9.
數列:5,9,13,17,21,25,……
43 43
-86 d = = 18, d= 489

Answer 1

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lalala1563005

a1+a2+a44+a45=-28
a1+a45=a2+a44=-14
S45=45×(-14)÷2=-315