Question

if in an A.P., sum of n terms is - 3n², find its common difference

Answer 1

Since sum of n terms is 3n^2.

Then ,

Sum of first term would be

S1 = 3 × 1^2 = 3

Therefore first term is 3 .

Sum of first two terms is

S2 = 3 × 2^2 = 3×4 = 12

Second term = 12 - 3 = 9 .

Hence common difference = 9 - 3 = 6.

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