Q. 75.0( 1 Vote )

A geometric series consists of four terms and has a positive common ratio. The sum of the first two terms is 9 and sum of the last two terms is 36. Find the series.

Let the first term = a

And common ratio = r

Series : a, ar, ar2, ar3

a + ar = 9

a(1 + r) = 9 ………………(1)

ar2 + ar3 = 36

ar2(1 + r) = 36

9r2 = 36 ( From Equation (1))

r2 = 4

r = 2

Putting the value of r in (1),

a(1 + 2) = 9

3a = 9

a = 3

Series : 3 + 6 + 12 + 24

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