InterviewSolution
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InterviewSolution
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e 99 The sum of the first n terms of an AP whose first term is 8 and the commonderence is 20 is equal to the sum of the first 2n terms of another AP whose first term is-30Exemplar Problem]ad the common difference is 8. Find n |
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Answer» Sum of n terms of AP= n/2(2a + (n-1)d) For AP whose first term a = 8 and common difference d = 20. Sum of first n terms Sn = n/2 (2*8 + (n - 1)20) Sn = n/2(16 + 20n - 20) Sn = n(10n - 2) For AP whose first term a = 30 and common difference d = 8. Sum of first 2n terms S2n = 2n/2 (2*-30 + (2n - 1)8) S2n = n(-60 + 16n - 8) S2n = n(16n - 68) Given, Sn = S2nn(10n - 2) = n(16n - 68)6n = 66n = 66/6 = 11 Value of n = 6 |
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