1.

The sum of first two terms of an infinite G.P. is 5 and each term isthree times the sum of the succeeding terms. Find the G.P.

Answer» Let the G.P. is `a, ar,ar^2...oo`
Here, `a` is the first term and `r` is the common ratio.
Then,
`a+ar = 5`
Also,
`T_n = 3(T_(n+1)+T_(n+2)+...oo)`
`=>ar^(n-1) = 3(ar^n+ar^(n+1)+...oo)`
`=>ar^(n-1) =3ar^n(1+r+r^2...oo)`
`=>1 = 3r(1/(1-r))`
`=>1-r = 3r`
`=>4r = 1`
`=> r = 1/4`
`:. a +a(1/4) = 5`
`=>5/4a = 5`
`=> a= 4`
So, G.P. is `4,1,1/4,1/16...oo.`


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