Question

A geometric progression has common ratio = 3 and last term = 486. If the sum of its terms is 728; find its first term.

Answer 1

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.