Question

what is the formula for calculating Sn​

Answer 1

Sn = n/2 ( 2a (n - 1) d )

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Answer 2

Answer:

Sn = a + (a + d)+(a + 2d) + ... + (ℓ − 2d)+(ℓ − d) + ℓ. 2 n(a + ℓ) . We have found the sum of an arithmetic progression in terms of its first and last terms, a and ℓ, and the number of terms n.