Question

The 14th term of an AP is twice its 8th term. If
its 6th term is -8, then find the sum of its first

20 terms.

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Answer 1

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Answer 2

The 5th term of a GP is ar^4 = 81 …(1)

The 8th term of a GP is ar^7 = 2187 …(2)

Divide (2) by (1) to get

r^3 = 2187/81 = 27, or

r = 3 and a = 1

The GP has the first term as 1 and the common ratio as 3.

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