Mathematics
Find the sum of first 22 terms of an A.P. in which d = 7 and a22 is 149.
AP GP
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Answer
Given, d = 7 and a22 = 149.
By formula, an = a + (n - 1)d
⇒ 149 = a + (22 - 1)7
⇒ 149 = a + 21(7)
⇒ 149 = a + 147
⇒ a = 149 - 147
⇒ a = 2.
By formula Sn =
⇒ Sn =
⇒ Sn = 11[4 + 147]
⇒ Sn = 11 × 151
⇒ Sn = 1661.
Hence, the sum of first 22 terms of the A.P. is 1661.
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