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

1. experimentX Group Title

Sinf??

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

3. experimentX Group Title

you should have written more explicitly

what do u mean ?

5. experimentX Group Title

sum up to infinity

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 ).

lol ,thats all what I know xD

I think its we can apply the rule only ..

9. experimentX Group Title

put n=2 ...

10. experimentX Group Title

1/r + 1 = 8

11. experimentX Group Title

find the value of a from the left relation

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

13. experimentX Group Title

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

14. experimentX Group Title

ignore that post ... i wasn't thinking

nvm :)

sry for asking many questions :/

17. experimentX Group Title

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

aha...

@satellite73 : can u help :)

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

21. experimentX Group Title

from your second relation ... put n=2

oh, OK

23. experimentX Group Title

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

24. experimentX Group Title

*get the value of a