Question

Ci

求解 急！！

tild
16d =12
==38+161
3 lid = 15
d=2 / 12
羅漢數學專業用心
X (44+ £X-2) = 25
X[X²]
X = -√3+(1-1) + 34
3x +59x + 17 =0
n=
MA
8.
X = -√2+1-4
(5分)有一等差級數,前 20 項的總和為-18,前4n項的總和為12,求前 8n 項的總和
為何?
2n [sal+(n-1)d]
4n [Jal+ (Art)!
=-18
E
In [salt (an-Dd] =336
4n [2al+ (4h-Dd] =14
76
54nal +4n²-³h = -36
28nal+lon² - 161 = 14
X-87. —
Anal+ 12+ -14h
18+12= 30
30+1=5
12+30= 41
216
A = 42

國中數學講座、代數篇
蘿 漢老師 楊授
【數列與級數
5. (6分)等差級數前 20 項的和為 1000,第 21 項到第 50 項的和為 6000,求該級數前 80
項的和為何?
sol Ja/119))
1600
= 30 [261+19]] = 2000
18400
(6分)等差級數(-25)+(-22.5)+(-20)+..
則:
(1)求此等差級數到第7項的和=?
(2)求此差級數前n 項的和為-135,求n之值=?43-9013/4)
(1)
-225-(-25)
23
(2) h[=-50+ (14) 25-35 ==-735+ (5)
ht=50+154²-2.5]35 ==1705 +
ME 15M=515] = 137 15
万