(6) Sn =
(-1)"
2n
(iii) S8 - S4
(i)n=1のとき
16
8
A₁ = S₁ =
- =
1
S
2
I
16
(ii)n=2のとき
An= Sn-Sn-1
=
(-1)^(-1)^²-1
2(n-1)
2n
{2(n-1)(-1)}-{2n (-1)^²-¹3
2n {2(n-1)}
{ (2n-2)(-1)^} - {2n(-1)^- (-1)]}
2n (2n-2)
(2n-2) (-1)^+ 2n(-1)^ (-1)^ {(2n-2) +2n}
4n²-4n
4n (n-1)
(-1)^(4n-2)
(-1)^²- &(2n-1) (-1)"^ (2n-1)
An(n-1)
2n(n-1)
4n (A-T)
(-1)^(2n-1)
JX£ $²), A₁ =) = 2.
(n=2)
2n(n-1)
H
1
(5) an = 2.3-1-2"-¹(n ≥ 1), S
=
Answer 4 (4) an
-(n ≥ 1), S =
4n² - 1
153
(1) 5,10,15,20,25,30, 35 公差 5 (2) 32,25,18,11,4,-3,-10 公差 -7(3) 30,50,70,
11
½. an.
[
16
(3)
(4)
