in a gp,a=1,r=-2/3,sn=55/81.find n
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r<1
therefore
Sn=a(1-r^n)/(1-r)
55/81=1*(1-r^n)/1-r
put values of r
55/81(1+2/3)=1-(-2/3)^n
55/81+110/243=1-(-2/3)^n
Taking lcm
(165+110)/243=1-(-2/3)^n
265/243=1-(-2/3)^n
taking one on lhs
265-243/243=-(-2/3)^n
22/243=-(-2/3)^n
I think there is a issue with the question pls check is it a infinite gp if it is I shall recorrect my answer
therefore
Sn=a(1-r^n)/(1-r)
55/81=1*(1-r^n)/1-r
put values of r
55/81(1+2/3)=1-(-2/3)^n
55/81+110/243=1-(-2/3)^n
Taking lcm
(165+110)/243=1-(-2/3)^n
265/243=1-(-2/3)^n
taking one on lhs
265-243/243=-(-2/3)^n
22/243=-(-2/3)^n
I think there is a issue with the question pls check is it a infinite gp if it is I shall recorrect my answer
Anonymous286:
did u check?
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