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kmeds16
Group Title
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.
 2 years ago
 2 years ago
kmeds16 Group Title
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.
 2 years ago
 2 years ago

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

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

hitten101 Group TitleBest ResponseYou've already chosen the best response.0
n is 10 not 4
 2 years ago

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

kmeds16 Group TitleBest ResponseYou've already chosen the best response.0
@hitten101 yes yes :)
 2 years ago

shubhamsrg Group TitleBest ResponseYou've already chosen the best response.2
you 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..
 2 years ago

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

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

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

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

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

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

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

shubhamsrg Group TitleBest ResponseYou've already chosen the best response.2
ahh k..got it
 2 years ago

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

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

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

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

shubhamsrg Group TitleBest ResponseYou've already chosen the best response.2
seems likely..
 2 years ago

shubhamsrg Group TitleBest ResponseYou've already chosen the best response.2
do 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.. :)
 2 years ago

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

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