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Question
In an A.P. a = 2 and d = 3, then find S12.
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Solution
a = 2 and d = 3 ...[Given]
Since `S_n = n/2 [2a + (n - 1)d]`,
`S_12 = 12/2 [2(2) + (12 - 1)(3)]`
= 6[4 + 11(3)]
= 6(4 + 33)
= 6(37)
= 222
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