## anonymous 4 years ago An Infinite Geometric sequence Such : $S \infty =81/2 , Sn/Tn=(3^n-1)/2$ ,Find The G.s ???

1. experimentX

Sinf??

2. anonymous

Sum to infinity :D Its rule is S∞ =a/1-r .

3. experimentX

you should have written more explicitly

4. anonymous

what do u mean ?

5. experimentX

sum up to infinity

6. anonymous

An infinite geometric series is an infinite series whose successive terms have a common ratio. Such a series converges if and only if the absolute value of the common ratio is less than one ( | r | < 1 ).

7. anonymous

lol ,thats all what I know xD

8. anonymous

I think its we can apply the rule only ..

9. experimentX

put n=2 ...

10. experimentX

1/r + 1 = 8

11. experimentX

find the value of a from the left relation

12. anonymous

u mean 1-r ,but why u put a =1 ?

13. experimentX

Oh ... sorry ... forgot to divide by 2

14. experimentX

ignore that post ... i wasn't thinking

15. anonymous

nvm :)

16. anonymous

sry for asking many questions :/

17. experimentX

$\frac{S_2}{T_2} = 4 = \frac{a +ar}{ar}$ find the value of r from here get the value of a from other relation

18. anonymous

aha...

19. anonymous

@satellite73 : can u help :)

20. anonymous

@experimentX :from where u got that 4 in Sn/Tn=4=... ?

21. experimentX

from your second relation ... put n=2

22. anonymous

oh, OK

23. experimentX

you will get the value of r from here use your first relation to get the second value

24. experimentX

*get the value of a

25. anonymous

oh ,k........TY ^.^_^.^

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