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RQW@ @pþÝn¾aì@pbÉibnn¾a

r =1 an = a1rn−1 ()
3
9, 3,1, 1 , 1,…
39

.a1 = 9

 1 n −1
3
an = a1r n−1 = 9 × = 32 × 3−n+1 = 33−n

.n ≥ 1 an = 33−n

k, 3k,20 − k ()

k

3k = 20 − k .k = 2
k 3k ()
3 = 20 − k

3k
9k = 20 − k
10k = 20

6, 6 2, 12, 12 2, …

. 1400

( ).an = 6 × n−1 .r = 2 a1 = 6

2