Question

the sum of n terms in A.p is 5n-n^2 find the first term and the common difference

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Answer 1

We know that, sum of first n terms = Sn = [2a + (n − 1)d] It is given that sum of the first n terms of an A.P. is 5n − n2. ∴ First term = a = S1 = 5(1) − (1)2 = 4. Sum of first two terms = S2 = 5(2) − (2)2 = 6. ∴ Second term = S2 − S1 = 6 − 4 = 2.