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Question
A geometric progression has common ratio = 3 and last term = 486. If the sum of its terms is 728; find its first term.
Solution
For a G.P.,
Common ratio, r = 3 ...(∵ r > 1)
Last term, l = 486
S = 728
`=> (lr - a)/(r - 1) = 728`
`=> (486 xx 3 - a)/(3 - 1) = 728`
`=> (1458 - a)/2 = 728`
`=>` 1458 – a = 1456
Hence, the first term is 2.
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