The first term of an infinite geometric progression is -8 and the second term is 6. What is the sum of all the positive terms?
我識得條式,,,,但係我諗緊佢係positive terms 係咪應該除2
但係應該點,,因為我除左2個ans唔岩,,我應該點做,.,,ans 係96/7
plz
Form 4 maths
2008-11-19 5:26 am
回答 (1)
2008-11-19 5:50 am
✔ 最佳答案
The G.P.: -8, 6 ............
The first term = -8
The common ratio = 6/(-8) = -3/4
The G.P.: -8, 6, 6(-3/4), 6(-3/4)2, 6(-3/4)3, 6(-3/4)4, ........
The positive terms form a new G.P.:
The first term of the new G.P., a = 6
The common ratio of the new G.P., r = (-3/4)2 = 9/16
Sum of all the positive terms
= a / [1-r]
= 6 / [1-(9/16)]
= 6 / (7/16)
= 6 x (16/7)
= 96/7
=
收錄日期: 2021-04-13 16:15:06
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