過程
o e al 33 = 4 + (8 1X(-1) = -8
範例 7
B-X
V
演練7
設有兩個等差數列,其前項總和的比為
(5m +6):(3n +1),試求此兩數列的第13項
的比
ba
【基隆女中)
LED
an
設有兩個等差數列,其第n 項的比為
(5n +6):(3n +1),試求前13項總和的比,
解
a 75 = 5+6=11
b = = 3+|=4
n=9, taztueta 13
+
o
TO
zl
( (5x1+6)+(5x2 +6) + (5 8346)41, +(5X13+)
= 6x43 +5
= 78 +5x13x7 =537
(3x/+1) +(3x2+1) Xin + ( 3x1371)
((
|+ 3
40=bit het
+ biz
+(
92 = 2q -S, = (1076)-11 = 5-sd-6
b2 = 5=-3,= 6+1 -4 =3> d=(-1)
=IxB + 3 (2.GA
533
= ibtdby
= 286
131:76 1 = 13 + 3x3
286
類題7
4:22
an
設有兩個等差數列{an},{b.〉,且滿足
-
2n +3
若兩數列前n项和分別為S., Sh',則
6n + 4'
be
Sil: Siu's
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