@ @¶ìÿa@óÝy‹¾a@ u@ @RQV
3 + 5d = 12
5d = 9
d = 9 = 1.8
5
. 3, 4.8, 6.6, 8.4, 10.2, 12
[Geometric Sequences] (.)
.(common ratio) {an }
r an +1 = anr
.n
4, 12, 36, 108, …
.3
4, − 12, 36, − 108, …
.−3
.c a b =a cba
cb
b2 = ac ac
b = ± ac {an }
(geometric mean)
r
a1, a1r, a1r 2, a1r 3, …, a1r n−1, …