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Find the sum of first 24 terms of the AP : 5, 8, 11, 14, ......... . |
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Answer» Given AP is 5, 8, 11, 14, ….. First term of given AP is a = 5. Common difference of given A.P is d = a2 – a1 = 8 – 5 = 3. We know that sum of first n terms of AP whose first term is a and common difference is d is given by Sn = \(\frac{n}{2}\) [2 + ( − 1)]. Therefore, the sum of first 24 terms of the given AP is S24 = \(\frac{24}{2}\) [2 × 5 + (24 − 1)3] = 12[10 + 23 × 3] = 12(10 + 69) = 12 × 79 = 948. (∵ a = 5, d = 3, n = 24) Hence, the sum of first 24 term of given AP is 948. |
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