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

Question

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

experimentx · Answer

Sinf??

anonymous · Answer

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

experimentx · Answer

you should have written more explicitly

anonymous · Answer

what do u mean ?

experimentx · Answer

sum up to infinity

anonymous · Answer

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 ).

anonymous · Answer

lol ,thats all what I know xD

anonymous · Answer

I think its we can apply the rule only ..

experimentx · Answer

put n=2 ...

experimentx · Answer

1/r + 1 = 8

experimentx · Answer

find the value of a from the left relation

anonymous · Answer

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

experimentx · Answer

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

experimentx · Answer

ignore that post ... i wasn't thinking

anonymous · Answer

nvm :)

anonymous · Answer

sry for asking many questions :/

experimentx · Answer

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

anonymous · Answer

aha...

anonymous · Answer

@satellite73 : can u help :)

anonymous · Answer

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

experimentx · Answer

from your second relation ... put n=2

anonymous · Answer

oh, OK

experimentx · Answer

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

experimentx · Answer

*get the value of a

anonymous · Answer

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