Jawapan

2016-02-28T12:03:07+08:00
A = 2
r = 3/2

sn > 80
2 ( 1 - 3/2^n ) รท ( 1 - 3/2) > 80
2 ( 1 - 3/2^n ) > -40
( 1 - 3/2^n ) > -20
-3/2^n > -21
n log 3/2 < log 21
n < 1.14
n = 1
1 5 1