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If sun of first n terms of an A.P. is 2n2 + 7n, write its nth term |
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Answer» Given, Sn = 2n2 + 7n We know that, an = Sn − Sn-1 ∴ an = 2n2 + 7n − {2(n − 1)2 + 7(n − 1)} = 2n2 + 7n − {2(n2 − 2n + 1) + 7n − 7} = 2n2 + 7n − {2n2 − 4n + 2 + 7n − 7} = 4n + 5 |
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