If the sum of first 7 terms of an AP is 49 and that of 17 terms is 289, find the sum of first n terms.

Question

Philoid · Accepted Answer

This is not in GP

Since they have given common difference -2

But need here is common ratio in GP series

(OR)

They have said that successive steps need 2 bricks less than the previous.

If we write the number of bricks used for each steps

100, 100-2, 100-4,……100-48

100, 98, 96,…..52

Common ratio = r₁ = = =

r₂ = = =

since the common ratios are not equal they are not in GP