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kmeds16
 2 years ago
Given a geometric sequence whose sum of the first 10 terms is 4 and whose sum from the 11th to the 30th term is 48, find the sum from the 31st to the 60th term.
kmeds16
 2 years ago
Given a geometric sequence whose sum of the first 10 terms is 4 and whose sum from the 11th to the 30th term is 48, find the sum from the 31st to the 60th term.

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cwrw238
 2 years ago
Best ResponseYou've already chosen the best response.0Sum of 10 = a * (r^4  1)  = 4 r 1

kmeds16
 2 years ago
Best ResponseYou've already chosen the best response.0@cwrw238 why is it r^4? I thought it's r^10.

amistre64
 2 years ago
Best ResponseYou've already chosen the best response.0hmm, given is: \[S_n=\frac{1r^n}{1r}\] \[S_{10}=4=\frac{1r^{10}}{1r}\] \[S_{3010}=48=\frac{1r^{20}}{1r}\]

shubhamsrg
 2 years ago
Best ResponseYou've already chosen the best response.2you have been given the sum upto first 10 terms =4 you have also been given the sum upto first 30 terms = 4 + 48 =52 and you have 2 eqns with 2 variables >solve for a and r now calculate sum for first 60 terms from that subtract sum of first 30 terms.. this should help..

hitten101
 2 years ago
Best ResponseYou've already chosen the best response.0dw:1351514867224:dw

kmeds16
 2 years ago
Best ResponseYou've already chosen the best response.0a(r^10  1) / r  1 = 4 a(r^30  1) / r  1 = 52 ? @shubhamsrg like this?

hitten101
 2 years ago
Best ResponseYou've already chosen the best response.0solve for a and r.. then find the sum of 60 terms subtract sum of 30 terms from sum of 60 terms

shubhamsrg
 2 years ago
Best ResponseYou've already chosen the best response.2@kmeds16 yep @hitten101 mistake in your formulla in the denominator..

kmeds16
 2 years ago
Best ResponseYou've already chosen the best response.0I got, r^10 = 3. this is confusing :/ 10th root of 3?!

cwrw238
 2 years ago
Best ResponseYou've already chosen the best response.0my mistake r^10 not r^4

shubhamsrg
 2 years ago
Best ResponseYou've already chosen the best response.2how'd you get that? o.O

hitten101
 2 years ago
Best ResponseYou've already chosen the best response.0@kmeds16 @shubhamsrg yes no exponent in the denominator.. you are right

kmeds16
 2 years ago
Best ResponseYou've already chosen the best response.0second equation divided by first equation. hehehehehe

shubhamsrg
 2 years ago
Best ResponseYou've already chosen the best response.2your main aim is not to find r,, your main aim is to find sum.. leave it as r^10 = 3

kmeds16
 2 years ago
Best ResponseYou've already chosen the best response.0find the sum of S60 and subtract 52, right?

shubhamsrg
 2 years ago
Best ResponseYou've already chosen the best response.2do this,,this might simplify.. substitue r^10 =3 whereever you can leave r1 as it is.. you can see a/(r1) = 4/(r^10 1) in calculation for sum of 60 terms ,make use of this eqn,, no need to find a.. :)

shubhamsrg
 2 years ago
Best ResponseYou've already chosen the best response.2r^60 we all can find.. hmm.. hope that helped..

kmeds16
 2 years ago
Best ResponseYou've already chosen the best response.0solving...hehehe ahm, thanks for the idea..
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