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Question
Find the sum of the first 22 terms of the A.P. : 8, 3, –2, ………
Solution
The given A.P. is 8, 3, –2, ………
Here, a = 8, d = 3 – 8 = –5 and n = 22
∴ `S = n/2[2a + (n - 1)d]`
= `22/2 [2 xx 8 + (22 - 1) xx (-5)]`
= 11[16 + 21 × (–5)]
= 11[16 – 105]
= 11 × (–89)
= –979
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