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प्रश्न
Write the formula of the sum of first n terms for an A.P.
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उत्तर
Sum of the first n terms is given by
Sn = `"n"/2[2"a" + ("n" - 1)"d"]`,
where a = first term,
d = common difference
OR
Sn = `"n"/2("t"_1 + "t"_"n")`,
where t1 = first term,
tn = last term
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