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Question
Write the formula of the sum of first n terms for an A.P.
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Solution
Sum of the first n terms is given by
`S_n = n/2[2a + (n - 1)d]`,
where a = first term,
d = common difference
OR
`S_n = n/2(t_1 + t_n)`,
where t1 = first term,
tn = last term
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