Question

The algebraic form of the sum of the first n terms of an arithmetic sequence is 2n2+8n .how many consecutive terms of the sequence starting from the first are to be added to get 300?

Answer 1

Step-by-step explanation:

Sn = 2n2 + 8n (Given) 330 = 2n2 + 8n 2n2 + 8n – 330 = 0 n2 + 4n – 165 = 0 n2 + 15n – 11n – 165 = 0 n(n + 15) – 11 (n + 15) = 0 (n + 15) (n – 11) = 0 If n + 15 = 0 ⇒ n = – 15 (terms are not negative) n – 11 = 0 ⇒ n = 11 ∴ Hence, total 11 term from starting to be added.Read more on Sarthaks.com - https://www.sarthaks.com/212360/the-algebraic-form-for-the-sum-of-first-n-terms-of-an-arithmetic-sequence-is-2n-2-8n?show=212367#a212367