Example 11 - Find sum of first 22 terms of AP: 8, 3, -2, .. - Finding sum of n terms

  1. Chapter 5 Class 10 Arithmetic Progressions
  2. Serial order wise
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Example 11 Find the sum of the first 22 terms of the AP : 8, 3, –2, . . . 8,3, –2,………… We have to find sum of first 22 terms . Sum = 𝑛/2 (2a + (n – 1) d) Here n = 22, a = 8 d = 3 – 8 = – 5 Putting there values in formula, Sum = 𝑛/2 [2𝑎+(𝑛−1)𝑑] = 22/2[2×8+(22−1)(−5)] = 11[16+(21)(−5)] = 11[16−105] = 11[− 89] = – 979

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