8) It sn denotes the sum of n terms of an A.P. whose common difference is d then show that 2 sn - 25n-1 + sn-2 sn-2
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Sn = n2[2a + (n - 1)d] Sn + 2 = (n + 2)2(2a + (n + 2 - 1)d] = n + 22(2a + (n + 1)d) To find Sn - 2Sn + Sn + 2 = - Sn + Sn + 2 = ( - n2 )[2a + (n - 1)d]
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(2a +(n- 1 )d)
hope it will help you
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